Java Tutorial

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Java Loops

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Java Programs

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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 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

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Java Serialization Java transient

Networking

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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 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

Java Differences

Java vs JavaScript Python vs Java Kotlin vs Java Java vs C++ C# vs Java Static vs Non-static in Java C vs Java int vs Integer in Java Stack vs Heap in Java Java Array vs ArrayList

How to

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 call a method in Java How to sort an array 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 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 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 achieve abstraction in Java How to call static method in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Parallel Arrays Sort in Java

Java 9 Features

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

Java Servlet Tutorial

Java Servlets Tutorial

Java JSP Tutorial

Java JSP Tutorial

Hibernate Tutorial

Hibernate Tutorial

Spring Tutorial

Spring Tutorial

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Spring MVC Tutorial

Jenkins Tutorial

Jenkins Tutorial

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.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

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 Char and String differences in Java Difference between String, StringBuffer and StringBuilder 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 calculate time difference in Java 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

Java Strings

String class is the most used class in Java programming language. The string is the sequence of characters, which is treated as objects in Java.

Creating String objects

We create String objects using a new operator or by using string literal values within double quotes. But there is a big difference between them about how these objects are stored and referred to, by Java.

Example 1.

public class ExampleString {
public static void main(String[] args) {
StrObj stringClass = new StrObj();
System.out.println(stringClass.str1 == stringClass.str2);
}
}
class StrObj {
String str1 = new String("INDIA");
String str2 = new String("INDIA");
}

Output:

false

String objects created using new operator always refer to separate objects, even if they store the same sequence of characters.

Example 2.

public class ExampleString {
String str1 = "INDIA";
String str2 = "INDIA";
public static void main(String[] args) {
ExampleString stringClass = new ExampleString();
System.out.println(stringClass.str1==stringClass.str2);
}
}

Output:

true

When the string object is created using literal method, JVM searches for the same sequence of character in the string pool. If it finds the same sequence, JVM does not create the string object but make it refer to the same string previously created. Hence str2 will point to the object created by the str1 that’s why the result is true here.

We can also create a string object using

System.out.println("INDIA");

If the matching value is found in the string pool, the value is reused. If the matching value is not found in the string pool, JVM has first to create it and then place it to the spring pool.

Let's count some string objects:

1 String star = new String("Star");
2 String star2 = "Star"; 
3 System.out.println("Star");
4 System.out.println("Moon");
5 System.out.println("Moon" == "star");
6 String star1 = new String("Star");

Line 1 creates a String object having value “Star” in heap memory.

Line 2 creates a String object and place it to the string pool.

Line 3 does not create String object since the same value is stored in the string pool.

Line 4 creates a String object having value “Moon” and place it to the string pool.

Line 5 creates String object since “star”  has a lower case ‘s’ and it is treated as a different value.

Line 6 creates a String object having value “Star” in heap memory.

String class is Immutable

String class is immutable, and it means that the object of this class can not be modified.

This is for performance reason, and the JVM can reuse this object which led to low memory overhead and good performance.

String class is made immutable by following three steps.

  • The value of the String object is stored in the char array (char value[]) and it is marked final so that it cannot be modified or re-initialized.
  • The length of the array is fixed and cannot be increased once initialized.
  • All methods defined in the string class do not modify the array value instead, they return a new String object.

Methods of the String Class

charAt(): It is used to retrieve a character at a specified index of a String :

Example:

public class Myclass{ 
public static void main(String args[]){ 
String country = new String("India");
System.out.println(country .charAt(0)); //  returns “I”
System.out.println(country .charAt(3)); // returns “i”
    } 
}

Output:

I
i

This method may throw a runtime exception if we seek the position out of the range

Example:

System.out.println(country.charAt(5));

the exception is java.lang.StringIndexOutOfBoundsException.

indexOf():  This method search for the occurrence of a character or a String, if it found in the target String, it returns the first matching position else -1.

Example :

public class MyClass {
public static void main(String[] args) {
String country = "INDIA";
System.out.println(country.indexOf('D')); // prints 2
System.out.println(country.indexOf("I")); // prints 0
}
}

Output:

2
0

By default, JVM starts searching from index position 0 if we want to start searching at some specific position we may pass it like

public class MyClass {
public static void main(String[] args) {
String country = "INDIA";
System.out.println(country.indexOf('I', 2)); //prints 3
}
}

Output:

3

substring(): It returns the substring of the targeted string. It is of two kinds,

Example :

public class MyClass {
public static void main(String[] args) {
String country = "INDIA";
String sub = country.substring(2);  // prints DIA
String sub1 = country.substring(2,4); // prints DI
System.out.println(sub);
System.out.println(sub1);
}
}

Output:

DIA
DI

The first output will print from seeking the position to the end of the given string.

The second will print from seeking position to the last value-1(does not include the character at the end position).

It should be noted that the total length of the resulted string is

(end Index) - (beginning Index).

trim(): This method removes the leading and trailing whitespace and returns a new string.

Example :

public class MyClass {
public static void main(String[] args) {
String str = "  This Is Text    ";
System.out.println(str);       // prints “  This Is Text    ”
System.out.print(str.trim()); // prints “This Is Text”
}
}

Output:

This Is Text    
This Is Text

replace('a', 'A'): This method replaces all the specified occurrence of a char value with another value. We can also replace String with another String.

Example :

public class MyClass {
public static void main(String[] args) {
String country = "INDIA";
System.out.println(country.replace('I', 'A'));  // prints ANDAA
System.out.println(country.replace("DI", "LI")); //prints INLIA
}
}

Output:

ANDAA
INLIA

length() : length() method  is used to retrieve the length of a String.

Example :

public class MyClass {
public static void main(String[] args) {
System.out.println("India".length()); // prints 5
}
}

Output:

5

Equality of Strings

equals() method is used to compare the equality of two string. This method returns true if the object being compared to a string object and have the same characters sequence.

public class MyClass {
public static void main(String[] args) {
String v1 = new String("INDIA");
String v2 = new String("INDIA");
System.out.println(v1.equals(v2));     //prints true
System.out.println(v1 == v2);     //prints false
}
}

Output:

true
false

String Concatenation

A string can be concatenated using concat() or “+” operator.

str1.concat(str2)

or like

"INDIA".concat(" IS A COUNTRY") // prints INDIA IS A COUNTRY

or like

"INDIA"+"My Country" // prints INDIA My COUNTRY

Example:

public class MyClass {
public static void main(String[] args) {
String str1 = new String("INDIA");
String str2 = new String(" USA");
System.out.println(str1.concat(str2));
System.out.println( "INDIA".concat(" IS A COUNTRY"));   // prints INDIA IS A COUNTRY
System.out.println( "INDIA"+" Is My Country"); // prints INDIA My COUNTR
}
}

Output:

INDIA USA
INDIA IS A COUNTRY
INDIA Is My Country

Java String Methods List



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