Java Tutorial Index

Java Tutorial Java Features C++ vs Java Java History Java Hello World Java Development Kit Java Runtime Environment Java Virtual Machine Difference between JDK, JRE, and JVM Memory Areas in Java Java Operators Java Keywords Primitive Data Types Variables

Java Loops

Java Do While Loop Java While Loop Java For Loop Java Enhanced For Loop

Java Programs

Java Basic Programs Factorial Program in Java Fibonacci Series Program in Java Prime Number Program in Java Palindrome Number Program in Java Armstrong Number Program in Java Anagram Program in Java Pattern Programs in Java Calculator Program in Java Leap Year Program in Java Addition Program in Java Number Pattern Programs in Java Star Pattern Programs in Java Package Program in Java Pyramid Program in Java Sorting Program in Java String Palindrome Program in Java Even Odd Program in Java For Loop Program in Java If Else Program in Java Switch Case Program in Java GCD Program in Java LCM Program in Java Hello Program in Java Matrix Program in Java Menu Driven Program in Java Series Program in Java Client Server Program in Java Swapping Program in Java Pig Latin Program in Java Tower of Hanoi Program in Java Recursion Program in Java Matrix Multiplication Program in Java Perfect Number Program in Java Classes and Objects in Java Example Programs String Programs in Java Array Programs in Java Constructor Program in Java Inheritance Program in Java Abstract class Program in Java Interface Program in Java Encapsulation Program in Java Polymorphism Program in Java Exception Handling Program in Java Multithreading Program in Java Thread Program in Java Collection Programs in Java ArrayList Program in Java Stack Program in Java Applet Program in Java Swing Program in Java JDBC Program in Java How to run Java program in command prompt How to run Java program in Eclipse Program to find and replace characters on string in java Program to find the duplicate characters in a string Program to check whether a given character is present in a string or not Java Program to Print Permutations of String Java program to find frequency of characters in a string Java Program to remove duplicate characters in a string

Java Sorting

Sorting Algorithms in Java Merge Sort in Java Quick Sort in Java Bubble Sort in Java Insertion Sort in Java Selection Sort in Java Heap Sort in Java Radix Sort in Java Topological Sort in Java Bucket Sort in Java Counting Sort in Java

Java OOPs Concepts

OOPs - Object Oriented Programming Objects and Classes in Java Methods in Java Java Naming Conventions Constructors in Java Java this keyword Java static keyword Inheritance in Java Aggregation in Java Java super keyword Constructor Chaining and Constructor Overloading Java Polymorphism Static and Dynamic Binding in Java Java Abstraction Abstract class in Java Interface in Java Difference between Abstract class and Interface Java final keyword Packages in Java Access Modifiers in Java Java Wrapper classes Java Numbers Java Characters Java Integer Java Boolean Java Arrays Java Command Line Arguments Java strictfp Keyword Java Math

Java Strings

Java Strings Java String Methods StringBuilder in Java StringBuffer in Java Java Regular Expressions StringBuffer vs StringBuilder String vs StringBuffer String vs StringBuilder String Manipulation in Java Java String Concatenation How to Reverse a String in Java String Array in Java How to Compare Two Strings in Java How to Concatenate Two Strings in Java Why String in Immutable in Java java.lang.NumberFormatException for Input String String Pool in Java Java Generate Random String How to take String Input in Java Java String Interview Questions

Java Exceptions

Exception Handling in Java Java try catch Java throw Java throws Difference between throw and throws Java finally Java Custom Exception Java Exception Propagation

Garbage Collection

Automatic Resource Management in Java Java Garbage Collection Java finalize() Java gc() Difference between final, finally and finalize

Multithreading

Multithreading in Java Process and Thread in Java Basic Terms in Multithreading Java Thread creation Thread Scheduler in Java Java Thread class DeadLock in Java

Java IO

Java IO Java Read File Java file Reader Java Buffer Reader Java file Writer Java BufferedWriter Java InputStreamReader Scanner in Java Java StringReader Java StringReader Class Java StringWriter Class Java PrintWriter Java File Java Read File Line By Line Java FileInputStream Java FileOutputStream Java Create File Java Delete File Java Open File Java Read File to String Java copy file Jar File in Java Java FileNotFoundException

Serialization

Java Serialization Java transient

Networking

Java Network Programming Java Socket Programming Java URL Java URLConnection HttpURLConnection in Java Java InetAddress Java DatagramSocket and Java DatagramPacket

AWT

Java AWT

Swing

Swing in Java

Java Collections

Collections in Java Java List Interface ArrayList in Java LinkedList in Java Vector in Java Stack in Java ArrayList vs LinkedList in Java ArrayList vs Vector in Java Java Set Interface HashSet in Java LinkedHashSet in Java TreeSet in Java Java Queue Interface PriorityQueue in Java Deque in Java ArrayDeque in Java Java Map Interface HashMap in Java LinkedHashMap in Java TreeMap in Java Dictionary in Java Hashtable in Java Properties in Java Collections class in Java Java Comparable Java Comparator Comparable vs Comparator in Java

Java Generics

Generics in Java

Java Annotations

Annotations in Java

Java JDBC

Java JDBC Tutorial JDBC Architecture Types of JDBC Drivers JDBC vs ODBC Java Database Connectivity with MySQL Java Database Connectivity with Oracle Statements in java Prepared statement in Java Resultset in java Java ResultSetMetaData DatabaseMetaData in Java Callable Statement in Java Transaction Management in Java Design of JDBC

Java Differences

Java vs DotNET Java vs JavaScript Python vs Java Kotlin vs Java Java vs C++ C# vs Java Java float vs double Java vs Scala Java vs Go Java vs Golang Java Extends vs Implements Java vs Node.js Static vs Non-static in Java C vs Java int vs Integer in Java Java protected vs private Java vs Dot Net Stack vs Heap in Java Java Array vs ArrayList Java SE vs EE Class vs Object in Java Java vs Bedrock Difference between = = and equals ( ) in java Difference between C, C++, java HashMap Vs HashTable Checked vs Unchecked Exceptions in Java Difference between print() and println() in Java Differences between Lock and Monitor in Java Concurrency Differences between Set and List in Java How to calculate time difference in Java Char and String differences in Java Difference between String, StringBuffer and StringBuilder in java Difference between String and Char Array in Java Differences between Byte Code and Machine Code Difference between String Tokenizer and split Method in Java Difference between JIT and JVM in Java Difference Between Data Hiding and Abstraction in Java Difference between String Tokenizer and Split Method in Java Difference Between BufferedReader and FileReader Difference Between Thread.start() and Thread.run()

How to

How to convert String to String array in Java How to find length of integer in Java How to get Day Name from Date in Java How to open the Java control panel How to resolve Illegal state exceptions in Java How to reverse a linked list in java How to encrypt password in Java How to calculate time complexity of any program in Java How to check version of java in Linux How to enable java in chrome How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to add double quotes in a string in Java How to convert list to String in Java How to call a method in Java How to Set Environment Variables for Java How to sort an array in Java How to Create Immutable Classes in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to Create Singleton Class in Java How to create thread in Java How to find length of String in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to find the length of an Array in Java How to Read Java JSON file How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to create custom exception in Java How to import packages in Java How to run applet Program in Java How to take Array Input in Java How to achieve abstraction in Java How to call static method in Java How to compare characters in Java How to compare dates in Java How to create a linked list in Java How to download Eclipse for Java How to get ASCII value of char in Java How to get the current date and time in Java How to handle NullPointerException in Java How to initialize string array in Java How to Install Java on MAC How to run java program in ubuntu How to find characters with the maximum number of times in a string java How to Set Java_home in Linux How to Split the String in Java with Delimiter How to take Multiple String Input in Java using Scanner class How to uninstall the Java in Ubuntu How to Update Java How to add Elements in Array in Java How to avoid deadlock in java How to Split String by Comma in Java How to remove special characters from String in Java How to remove last character from String in Java How to Read XML Files in Java How to download and install Eclipse in Windows How to Create an API in Java How to Round Double Float up to Two Decimal Places in Java How to create a mirror image of a 2D array in Java How to set timer in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Type Annotations in Java Java Stringjoiner Class Parallel Arrays Sort in Java Bifunction in java 8 Java 8 filters list Java 8 Consumer Interface in Java

Java 9 Features

Java 9 Tutorial Java 9 Try With Resources Java 9 Interface Private Method

Java 12

What’s new in Java 12

Java 13

Java 13 New Features

Java 14

New Features of Java 14

Java 15

What’s New in Java 15

Java 16

Java 16

Java 17

What is new in Java 17

Java Servlet Tutorial

Java Servlets Tutorial

Java JSP Tutorial

Java JSP Tutorial

Hiberate Tutorial

Hibernate Tutorial

Spring Tutorial

Spring Tutorial

Spring MVC Tutorial

Spring MVC Tutorial

Jenkins Tutorial

Jenkins Tutorial Jenkins java net socket connection time out

Java Math Methods

Math.abs() Math.acos() Math.addExact() Math.asin() Math.atan () Math.atan2() Math.cbrt() Math.ceil() Math.copysign() Math.cos() Math.cosh() Math.decrementExact() Math.exp() Math.expm1() Math.floor() Math.floorDiv() Math.floorMod() Math.fma() Math.getExponent() Math.hypot() Math.IEEEremainder() Math.incrementExact() Math.log() Math.log10() Math.log1p() Math.max() Math.min() Math.multiplyExact() Math.multiplyFull() Math.negateExact() Math.nextAfter() Math.nextDown() Math.nextUp() Math.pow() Math.random() Math.rint() Math.round() Math.scalb() Math.signum() Math.sin() Math.sinh() Math.sqrt() Math.subtractExact() Math.tan() Math.tanh() Math.toDegrees() Math.toIntExact() Math.toRadians() Math.ulp()

Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

Java Convert String to int Java Convert int to String Java Convert String to long Java Convert long to String Java Convert String to float Java Convert float to String Java Convert String to double Java Convert double to String Java Convert String to Date Java Convert Date to String Java Convert String to Object Java Convert Object to String Java Convert String to char Java Convert char to String Java Convert int to long Java Convert long to int

Misc

List all files in a Directory in Java Nonagonal number in Java Null Pointer Exception in Java Package naming convention in Java Packages Program in java Pangram Program in Java PriorityBlockingQueue Class in Java Race Condition in Java Repdigit Numbers in Java Reserved Keywords in Java Rotate matrix by 90 degrees in Java Segment Tree in Java Sierpinski Number in Java Sort Dates in Java Thread Safety and How to Achieve it in Java Normal and Trace of a Matrix in Java Transient variable in Java Tribonacci series in Java Web Crawler in Java Zigzag Traversal of Binary Tree in Java Java Full Stack Java IO filenotfoundexception Java Output Formatting Java Plot Java Pop Java program to print matrix in Z form Java Set to List Java Switch string Java Thread Lifecycle: States and Stages Java Viva Questions and Answers Lazy Propagation in Segment Tree in Java Level order Traversal of a Binary Tree in Java Method chaining in Java Narcissistic Number in Java Java Case Keyword Java Try-Catch Block Java Class KeywordJava concurrency interview questions Java Continue Keyword Java CountDownLatch Java Default Keyword Java Double Keyword Java Editors Java Else Keyword Java Enum Keyword Java Extends keywordJava Finally Keyword Java Font Example of Static import in Java How Many Ways to Create Objects in Java Implementing Queue Using Array in Java Instanceof operator in Java Interchange Diagonal elements in Java Java Arrays Fill Java Char Keyword Convert list to array Java Convert milliseconds to date in Java Copy data/content from one file to another in java CRC Program in Java Creating a Jar file in Java Crown Pattern in Java Difference Between Access Specifiers and Modifiers in Java Difference Between Java and PHP Difference Between replace() and replaceall() in Java Duodecimal in Java Finding middle node of a linked list in Java Group by in Java 8 Hollow Diamond Pattern in Java How annotations work in Java Java Boyer Moore Catalan number in Java Cosmic Superclass in Java Difference between this and super in Java Fall through in Java Figurate Number in Java Java Anon Proxy Java RMI Lazy loading in Java Magnanimous Number in java Shallow copy in Java String to JSON in Java Tetranacci Number in Java Vigesimal in Java Why main method is static in Java Add Time in Java Bellman Ford Algorithm in Java Best Java Libraries Blockchain in Java Blocking Queue in Java Example Bully Algorithm code in Java Contextual keywords in Java Convert JSON File to String in Java Determine the Upper Bound of a Two-Dimensional Array in Java Java.net.ConnectionException Java.net.SocketException Web Service Response Time Calculation in Java Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java What are Array strings in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Replace character in string Java String Coding Interview Questions in Java What is String in Java? String isnullorempty in Java String Matches in Java Trim Method in String Java Bean class in Java Libraries in Java Arithmetic Operations on String in Java Convert Char array to string in java Check whether Java is installed or not How to stop execution after a certain time in Java Jagged Array in Java Java ArraylistRemove() Time Complexity Java Swing Time Picker Zigzag Array in Java Array and String based questions in Java Array and String with Examples in Java Best Practices to use String Class in Java What is string in Java why it's immutable Java String Java String Inbuilt functions Java String Matches vs Contains Sum of digits in string in java Check the presence of Substring in a String in java Java import packages Interfaces and Classes in Strings in Java Maximum length of string in java Hidden classes in Java Class memory in Java public static void main string args meaning in java Reverse a String in Java String Concatenation in Java Buffer reader to read string in Java Split String into String Array in Java Reverse a String using Collections in Java Upcasting and Downcasting in Java String Declaration in Java Method Overloading In Java Java Solid Principles Java Architecture Binary Search Java Star Program in Java Java Type Casting Java Pass-by-Reference Java Framework List Java Destructors Java Control Statements Java Byte Code Java Beans Java Identifiers Character Array in Java Java Applications Java Substring Java Session Non-primitive data types in Java Matrix Multiplication in Java JIT in Java Java Tokens Java Externalization Default Virtual Behaviour in C++ vs Java Why we use static in Java Session Tracking in Java Knapsack problem in Java Java Logo Java exception list Java Iterator Java instance variable Frugal number in Java Fork Join in Java Date time API in java Compile time vs Runtime in java Compare time in java AES 256 Encryption in Java Advanced Java skills What is advance Java? User Defined Exception in Java Upcasting in Java Tree Implementation in Java Special Operators in Java Reentrant Lock in Java Perfect Number in Java Java logger Java LinkedList vs ArrayList File Operation in Java Constructor Overloading in Java Conditional operator in Java Concurrent Linked Deque in Java with Examples Command Class in Java Java Break Keyword Best Java IDE Association in Java Access specifiers in Java AbstractSet Class in Java Adapter class in Java Composition in Java Mutable and Immutable in Java Static() Function in Java Traverse through HashMap in Java Vectors in Java Creation of Multi Thread in java Java Enumeration Compile-time Error in Java Java Get Time in UTC Java.sql.Time Format Structure of Java Program Thread Concept in Java Creation of Multi-Thread in Java Enterprise Java Beans POJO in Java Volatile keyword in Java Java Constant Collection Interfaces in Java with Examples Deadlock Prevention and avoidance in Java Java Boolean Keyword Java Byte Keyword Java List Implementations Java Xml Parser Method Overriding in Java RMI program in Java Virtual Function in Java What is interpreter in Java? Advanced Java Viva Questions Application of Array in Java Economical number in Java Iterate JSON array in Java Java callable example Java Command not found Java Date add Days Java File Extension Java Location Java Trim User Defined Custom Exceptions in Java Java array list remove time complexity Java.lang.Exception.NoRunnableMethods Java Map Example Java Obfuscator Java Pi Java Queue Java time local date Java Xmx Uses of Java Applet Life Cycle in Java Best Java Security Framework BigDecimal toString() in Java Jdoodle Java Literals in Java MVC in Java Powerful Number in Java Read the XLSX file in Java Relatively Prime in Java Root exception in java What is anagram in Java? Accessors and Mutator in Java Bottom view of a binary tree in Java Convert List to String in Java Equidigital in Java How to check data type in Java IdentityHashMap in Java Java Clone Array Java LDAP Authentication Java List Node Java Password Generator Magic Square in Java Pancake Sorting in Java Practical Number in Java Sublime Number in Java Sudoku in Java Compare Two Times in Java Diffie Hellman Algorithm in Java How to Reduce Time Complexity in Java Java calculate age Map of Map in Java Minimum XOR value pair in Java Palindrome Partitioning problem in Java Pernicious Number in Java Prime Points in Java Rectangular Numbers in Java Sleep Time in Java The final Keyword in Java Types of Statements in Java Unicode System in Java Zig Zag star and Number Pattern in Java Balanced Prime Number in Java ConcurrentSkipListSet in Java Construct the Largest Number from the Given Array in Java CopyOnWriteArrayList in Java Cyclic Barrier in Java Dangling Else problem in Java Display Unique Rows in a Binary Matrix in Java Empty Statement in Java Factorial of a Large Number in Java Facts about null in Java Rehashing in Java Singleton Design Pattern in Java Zebra Puzzle Problem in Java XOR of Array Elements Except Itself in Java Types of Sockets in Java Thread Synchronization in Java Set Up the Environment in Java Method and Block Synchronization in Java Fibodiv Number in Java House Numbers in Java GCD of Different SubSequences in Java Hogben Numbers in Java Decagonal Numbers in Java Converting Roman to Integer Numerals in java Check if the given array is mirror inverse in Java Caesar Cipher Program in Java Block Swap Algorithm for array rotation in Java Java Binary Tree Binary Strings Without Consecutive Ones in Java Beautiful Array in Java Balanced Parentheses in Java Arithmetic exception in Java Add numbers represented by Linked Lists in Java Two Decimal Places Java Intersection Point of two linked list in Java Find next greater number with same set of digits in Java Getter and Setter Method in Java Example Java Binary to Hexadecimal Java Calculate Average of List Iccanobif Numbers in Java Java delete directory Java For Keyword Java Float Keyword Java Instanceof Keyword Java If Keyword Java Int Keyword Java Import Keyword Java Package Keyword Java Static Keyword Java Public Keyword Java Implements Keyword Java Private keyword Java Protected Keyword Java Short Keyword Java Long Keyword Java Interface Keyword Java Try Keyword Java New Keyword Java Return Keyword Tug of War in Java Types of Events in Java

String Programs in Java

String Programs in Java: In Java, a String is an immutable object that represents a sequence of characters. For example, “Tutorial” is a string that consists of 8 characters: ‘T’, ‘u’, ‘t’, ‘o’, ‘r’, ‘i’, ‘a’, ‘l’. Immutable object means once a string is created, it cannot be changed, and if we try to change the string, we end up creating a new string. In this section, we will create different String programs.

The Java String class is used for the creating of a string object. However, we do not need to import the class String. This is because the Java String class is part of the java.lang package, and java.lang package is imported by default in every Java program. In Java, a string is represented by characters enclosed in double quotes (“”). For characters, single quotes are used (‘’);

Creating a String in Java

There are three ways of creating a string/ string object in Java:

  • Using string literal
  • Using the new keyword
  • Using a character array

Using string literal

FileName: StringExample.java

 public class StringExample
 {
                public static void main(String argvs[])
                {
                    // creating strings
                    String country = "India";
                    String country1 = "France";
                    String country2 = "Mexico";
                     // printing strings
                    System.out.println( country );
                    System.out.println( country1 );
                    System.out.println( country2 );
                }
 } 

Output:

 India
 France
 Mexico 

Explanation: In the above program, we have created three strings: country, country1 and country2 and assigned the strings: “India”, “France”, and “Mexico”. Note that we have not create any object of the class String. However, we know that a string is an object in Java. Hence, under the hood, JVM creates three objects for the three strings and assigns the reference to the string variables. Memory allocation for the three strings is done in the string pool ( a place in the heap memory used by JVM for avoiding string redundancy), whereas the string variables get placed in stack memory.

Using new Keyword

FileName: StringExample1.java

 public class StringExample1
 {
                public static void main(String argvs[])
                {
                    // creating strings using the new Keyword
                    String country = new String("India");
                    String country1 = new String("France");
                    String country2 = new String("Mexico");
                     // printing strings
                    System.out.println( country );
                    System.out.println( country1 );
                    System.out.println( country2 );
                }
 } 

Output:

 India
 France
 Mexico 

Explanation: In the above program, we have used the new keyword for creating the string object. The string objects are created in heap memory but not in the string pool. Memory for the string variables is allocated in the stack memory.

Using Character Array

FileName: StringExample2.java

 public class StringExample2
 {
                public static void main(String argvs[])
                {
                                // a character array
                                char arrChar[]={'A', 'm', 'e', 'r', 'i', 'c', 'a'};
                                // creating a string using the character array
                                String str = new String(arrChar);
                                // printing the string
                                System.out.println(str);
                }
 } 

Output:

America

Explanation: Using the given character array, we are creating string str. This time also, the new keyword comes in handy. Eventually, we are displaying the result.

The length() method

To calculate the size of a string, we use the length() method of String class. The signature of the method length() is:

public int length()

Since the keyword static is not used, the length() method cannot be invoked using the class name, i.e., String.length(). We have to use objects to call the length() method. It does not accept any parameter. It returns the length of the string. The following example illustrates the same.

FileName: StringExample3.java

 public class StringExample3
 {
                public static void main(String argvs[])
                {
                                int size; // for storing size of the input string
                                String s = "Apple"; // input string
                                // invoking the method length()
                                size = s.length();
                                // displaying the outcome
                                System.out.println("The size of the string \"" + s + "\" is " + size);
                }
 } 

Output:

The size of the string "Apple" is 5

Explanation: The string “Apple” internally gets converted to a character array. Then, the length field of the array is used to find its size, which is 5 in our case. The value of the length field is returned by the method length().

Manipulating Strings

Suppose we have a string s = “Apple”. The task is to change it to “Rpple”, i.e., instead of the letter ‘A’; we have to use the letter ‘R’. In c++, we can easily achieve the task. At the index 0, put the letter R, i.e., S[0] = ‘R’. But it is not possible in Java. Because strings are immutable. Therefore, we need to find a workaround to do the manipulation. One way is to use a character array. Observe the following Java program.

Using Character Array

 FileName: StringExample4.java

 public class StringExample4
 {
     public static void main(String argvs[])
     {
         String s = "Apple"; // input string
         int size = s.length(); // calculating size of the input string
         // creating a character array of the same size as the input string
         char ch[] = new char[size];
         // assigning characters from the input string
         // to the character array
         for(int i = 0; i < size; i++)
         {
             ch[i] = s.charAt(i);
         }
         ch[0] = 'R'; // updating character at the index 0
         // creating a new string using the character array
         s = new String(ch);
         // printing the new string
         System.out.println("The new string is " + s);
     }
 } 

Output:

The new string is Rpple

Explanation: We know that string is immutable in Java. However, the same is not true for arrays. This is why we need to generate a character array from the given input string. The above program does the same. First, the program allocates the size of the character array and then fills the array by scanning each and every character of the given string. In order to retrieve characters from the input array, the method charAt() is used. The method is defined in the class String. It accepts an int value as in its argument and returns the character present at that particular index. The signature of the method is:

public char charAt(int index)

If the value of the index is negative or greater than the size of the array, the method throws StringIndexOutOfBoundsException.

After assigning all the values to the character array, we update the value present at the index 0. Then, using the character array, we have created a string and assigned its reference to the same variable that was holding the input string. It means that the input string has no reference. Thus, the input string is ready for garbage collection. Eventually, we are displaying the result. Note that, at no place, we have manipulated the input string. We have to create a completely new string to get our result.

Using the replace() Method

Another approach is to use the predefined method replace(). The method is present in the class String. Observe the following Java program.

FileName: StringExample5.java

 public class StringExample5
 {
     public static void main(String argvs[])
     {
         String str = "Apple"; // input string
         // invoking the method replace()
         String strFinal = str.replace('A', 'R');
         // printing the new string
         System.out.println("The new string is " + strFinal);
     }
 } 

Output:

The new string is Rpple

Explanation: Instead of creating a character array, we have used the method replace() to accomplish our task. The replace() method, used in our code, takes two arguments: one is the character we want to replace (oldChar), and another is that character that replaces the oldChar (newChar). The signature of the replace() method is:

public String replace(char oldChar, char newChar)

From the signature, it is obvious that the replace() method returns a string. The replace() method creates a character array on the basis of the string upon which the method is called. In our code, str is calling the method. Thus, a character array is created of size equal to the length of string referred by str, which is 5. Then, all the occurrence of letter ‘A’ is replaced by ‘R’. From the character array a new sting a generated (similar to the previous example). The newly generated string is then returned, whose reference is being stored in the variable strFinal. Eventually, we are displaying the result. Thus, we see that even though we are using an in-built method, the immutability of the string remains intact.

Pattern Searching Program

In pattern searching, a word/ pattern and a text are given. The task is to find whether the given pattern is present in the text or not. For example, text = “llalalaland” and pattern = “land”. The pattern “land” is present in the text “llalalaland” at index 7. Observe the following code.

FileName: StringExample7.java

 public class StringExample7
 {
 public static void main(String argvs[])
 {
     // input text
     String text = "llalalaland";
     // finding text size
     int textSize = text.length();
     // pattern to be found in the input text
     String pattern = "land";
     // finding pattern size
     int patternSize = pattern.length();
     // for storing starting index of the pattern present in the text
     int index = -1; 
     // flag for indicating whether the pattern in found or not
     // in the input text
     Boolean isPatternFound = false;
     // We only iterate till that character of the input string,
     // from where we can accommodate the pattern. This is because a
     // pattern size can never be greater than input text size
     for(int i = 0; i < textSize - patternSize + 1; i++)
     {
         // from temp, we iterate to match the characters of text with pattern
         int temp = i;
         for(int j = 0; j < patternSize; j++)
         {
             if(text.charAt(temp) == pattern.charAt(j))
             {
                 // character matched!!
                 // check the next character of the pattern
                 temp++;
                 // assuming the pattern is found!!
                 isPatternFound = true;
             }
             else
             {
                 // character mismatch!!
                 // assumption made in if-block is not true.
                 isPatternFound = false;
                 // We have encountered a mismatch.
                 // No need to check further
                 break;
             }
         }
                 if(isPatternFound)
         {
             // pattern found!
             // updating the index
             index = i;
             // Since pattern is found,
             // there is no need to iterate further
             break;
         }
     }
     // printing the outcome
     if(isPatternFound)
     {
         System.out.println("The pattern \"" + pattern + "\" starts at index " + index + " in the text \"" + text + "\"");
     }
     else
     {
         System.out.println("The pattern " + pattern + "is not found in the text " + text);   
     }
 }
 } 

Output:

The pattern "land" starts at index 7 in the text "llalalaland"

Explanation: In the above program, we have used nested Java for-loop for finding the pattern. Inside the for loop, we have used the two pointers approach. One pointer is the outer loop variable i, for the given text, and another pointer is the inner loop variable j, for the given pattern. In each iteration of the outer loop, we assign the value of i to the variable temp. Because i marks the index, where we have to start the search of pattern in the text. Till this point, temp and i both point to the same index. Then, we enter the inner loop, where j is pointing to the first index of the pattern (j = 0).

Now, the comparison of characters of the text and the pattern starts. If the character pointed by temp matches with the character pointed by the j if-block of the inner loop gets executed. The variables j and temp are incremented by 1, and the flag isPatternFound is true. In the case of mismatch, the else block is executed, where the flag isPatternFound is assigned false value, and the inner loop is terminated.

Beneath the inner loop, there is an if block. The if block only gets executed if isPatternFound is true, which is only possible when the else block of the inner for loop is not executed at all. It means that the inner loop only leaves true value to isPatternFound when there is no mismatch. Inside the if-block, the index stores the value of the outer loop variable i, as i is the beginning index of the pattern matching in the text.

Let’s understand each iteration of the outer for-loop with the help of following steps.

For the 1st iteration of the outer loop,

i = 0, temp = 0, j = 0

llalalaland

land

The first character of the text matches with the first character of the pattern. Hence, the inner loop iterates once more.

i = 0, temp = 1, j = 1

llalalaland

land

The second character of the text does not match with the second character of the pattern. Hence, the else block of the inner block is executed, and the inner loop is terminated.

For the 2nd iteration of the outer loop

i = 1, temp = 1, j = 0

llalalaland

 land

The second character of the text matches with the first character of the pattern. Hence, the iteration continues of the inner loop.

i = 1, temp = 2, j = 1

llalalaland

 land

The second character of the pattern also matches. Therefore, temp and j again get incremented by 1.

i = 1, temp = 3, j = 2

llalalaland

 land

Now, we encounter a mismatch. Hence, the inner loop is terminated. Still, we did not find the pattern in the text. Therefore, the search continues.

For the 3rd iteration of the outer loop,

i = 2, temp = 2, j = 0

llalalaland

  land

In the first iteration of the inner loop, we get a mismatch. Hence, the inner loop terminates.

For the 4th iteration of the outer loop,

i = 3, temp = 3, j = 0

llalalaland

    land

The fourth character of the text matches with the first character of the pattern. Therefore, iteration of the inner loop continues.

i = 3, temp = 4, j = 1

llalalaland

    land

Again, the characters match. The inner loop iterates one more time.

i = 3, temp = 5, j = 2

llalalaland

    land

l ? n. Therefore, because of the mismatch, the inner loop terminates.

For the 5th iteration of the outer loop,

i = 4, temp = 4, j = 0

llalalaland

     land

a ? l. Hence, the inner loop does not iterate further.

For the 6th iteration of the outer loop,

i = 5, temp = 5, j = 0

llalalaland

       land

l = l. Therefore, temp and j are incremented by 1.

i = 5, temp = 6, j = 1

llalalaland

       land

Again, there is a match. Thus, we move to the next iteration of the inner for-loop.

i = 5, temp = 7, j = 2

llalalaland

       land

l ? n.  Because of the mismatch, the inner loop terminates.

For the 7th iteration of the outer loop,

i = 6, temp = 6, j = 0

llalalaland

         land

There is a mismatch. The control moves to the outer loop, again.

For the 8th iteration of the outer loop,

i = 7, temp = 7, j = 0

llalalaland

          land

The characters match. The inner loop iterates.

i = 7, temp = 8, j = 1

llalalaland

          land

Again, there is a match. The inner loop comes into the picture again.

i = 7, temp = 9, j = 2

llalalaland

          land

n = n. Still, there is a match. The inner loop iterates one more time

i = 7, temp = 10, j = 3

llalalaland

          land

The last character of the pattern matches and the inner and outer loop terminates. We see at i = 7; the successful search has occurred. Therefore, “index 7” is printed on the console. Therefore, we have successfully searched our pattern in the given text.



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