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

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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 BufferedWriter Java InputStreamReader Java File Java Read File Line By Line Java FileOutputStream Jar File in Java

Serialization

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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

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Java Servlets Tutorial

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Java JSP Tutorial

Hibernate Tutorial

Hibernate Tutorial

Spring Tutorial

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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

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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

Exception Handling Program in Java

Exception Handling Program in Java

Exception means something that is abnormal. In Java, an exception is treated as a problem that disrupts the normal flow of the program. An exception leads to abnormal termination of the Java program. There can be many scenarios where an exception can occur. A few of them are mentioned below.

  • When a number is divided by zero, for example, int x = 6 / 0; This statement is syntactically correct, but zero can never divide a number mathematically. Hence, an exception is raised.
  • Connecting to a server, but the server is off.
  • Opening a file, but the file is already deleted by someone.
  • Accessing the index that is not present in the array.
    For example, in the statement int arr[] = {7, 8, 9};, the array contains three elements arr[0], arr[1], arr[2], but if someone tries to access arr[10], then it is not possible as 10th index is not present in the array leading to the generation of an exception.
  • When JVM has run out of memory.
  • User is entering some invalid data. For example, someone types 1342 when asked to write his/ her name.

Some of the exception scenarios mentioned above are due to programmer error; some are due to failure of the resources, while others are due to user error.The exception handling program in Java demonstrates how to handle exceptions in order to maintain the natural flow of the program.

Hierarchical Structure of Exception in Java

Exception Handling Program In Java

All classes of exception are derived from the class java.lang.Exception, while the Exception class itself is the child class of the class Throwable. Errors are also the subtypes of the class Throwable.

The need of handling an Exception

Suppose there are 8 statements in a Java program, and an exception has occurred at the 4th statement. Due to exception, the normal flow of the program is interrupted that leads to abnormal termination of the program. Thus, the statements that are coming after the 4th statement never get executed. To ensure that statements after the 4th statement are executed, or to ensure the normal flow of the program, it is required to handle the exception that is raised due to the 4th statement.

Types of Exception in Java

Exceptions in Java can be categorized into the following three categories:

1) Checked Exception

2) Unchecked Exception

3) Error

Let’s discuss each type of exception in detail.

Checked Exception

Checked exceptions are those exceptions that are notified or handled during compile time. Therefore, these exceptions are also called the compile-time exception. These exceptions can never be ignored as it is generated during the compile-time. For example, if we try to access a file that is not present, it thows FileNotFoundException. Consider the following code.

FileName: FileNotFoundExceptionDemo.Java

 // import class FileReader
import java.io.FileReader;
// import class File
import java.io.File;
public class FileNotFoundExceptionDemo
{
// Driver Method
public static void main(String argvs[])
{                            
  // creating an fileObj using the text file path
  // along with its name
  File fileObj = new File("D:\\file.txt");
  // creating the object fr using the object fileObj
  // This object fr is used to read the file
  FileReader fr = new FileReader(fileObj);
  int rd;  
  // reading the file character by character
  // till the end of file
  while( (rd = fr.read()) != -1)  
  { 
    // printing the characters present in the file
               System.out.print( (char) rd);
  }
  // closing the filereader
  fr.close();   
}
} 

Upon compilation, the following exceptions are raised.

Output:

Exception Handling Program In Java

Explanation: We have seen that we never reached the execution stage because exceptions are raised during the compilation stage.  The methods read(), and close() are the methods of the class FileReader. These methods throw IOException, and the same has been notified by the Java compiler in the output.

Eliminating Checked Exception

We can use a try-catch block to eliminate the exceptions that came in the above-written program. The following code illustrates the same.

FileName: ExceptionHandleDemo.Java

 // import class FileReader
import java.io.FileReader;
// import class File
import java.io.File;
// Importing Exception classes FileNotFoundException & IOException
import java.io.FileNotFoundException;
import java.io.IOException;
public class ExceptionHandleDemo
{
// Driver Method
public static void main(String argvs[])
{             
  // creating an fileObj using the text file path
  // along with its name
  File fileObj = new File("D:\\file.txt");
  FileReader fr = null;
  try
  {
      // creating the object fr using the object fileObj
      // This object fr is used to read the file
      fr = new FileReader(fileObj);
  }
  // handling the FileNotFoundException
  catch(FileNotFoundException fe)
  {
      System.out.println("Inside the catch block of FileNotFoundException");
      fe.printStackTrace();
  }
  int rd;  
  try
  {
      // reading the file character by character
      // till the end of file
      while( (rd = fr.read()) != -1)  
      { 
        // printing the characters present in the file
               System.out.print( (char) rd);
      }
      // closing the filereader
      fr.close();
  }
  // handling the IOException & NullPointerException
  catch(IOException | NullPointerException ex)
  {
      System.out.println("Inside the catch block of NullPointerException & IOException");
      ex.printStackTrace();
  }
}
} 

Output:

Exception Handling Program In Java

Explanation: We have seen because of the statement fr = new FileReader(fileObj); FileNotFoundException is thrown. To handle the exception, the statement fr = new FileReader(fileObj); is put inside the try block, and the raised Exception is handled in the catch block. Similarly, NullPointerException and IOException are also handled. Observe that this time the termination of the program happened normally.

Unchecked Exception

Exceptions that are generated during the execution are called unchecked exception. These exceptions are also known as runtime Exception. These exceptions mainly occur because of some mistakes (logical mistakes, not proper usage of the API) done by the programmer/ developer. For example, if an array is declared of size 7, and the program is trying the access the 8th element, it generates an exception. The following program illustrates the same.

FileName: ArrayIndexExample.Java

 public class ArrayIndexExample
{
public static void main(String argvs[])
{
// declaring an integer array
int arr[] = {6, 7, 8, 6, 8, 0, 4};
// calculating size of the array
int size = arr.length;
// printing size of the array
System.out.println("Size of the array is " + size );
// displaying the 8th index of the array
System.out.println("The 8th index of the array is " + arr[8] );
}
} 

Output:

Exception Handling Program In Java

Explanation: In the array, the memory is allocated for the seven integers i.e. 0 to 6. Therefore, the 8th index goes beyond the range of indices of the array arr[]. Hence, we get the exception java.lang.ArrayIndexOutOfBoundsException. If we look at the code syntactically, we find that the statement System.out.println(“The 8th index of the array is ” + arr[8] ); is correct. The Java compiler interprets that the code is accessing the element that is present at the 8th index. However, the Java compiler has no idea about the memory allocation of the array. This is because memory allocation happens at the run-time. Therefore, we get the exception java.lang.ArrayIndexOutOfBoundsException at the run-time.

Handling Unchecked Exception

Similar to handling a checked exception, a try-catch blocks come in handy in handling unchecked too. The java.lang.ArrayIndexOutOfBoundsException raised in the above program can be handled by the following program.

FileName: ExceptionHandleDemo1.Java

 public class ExceptionHandleDemo1
{
public static void main(String argvs[])
{
// declaring an integer array
int arr[] = {6, 7, 8, 6, 8, 0, 4};
// calculating size of the array
int size = arr.length;
// printing size of the array
System.out.println("Size of the array is " + size );
try
{
    // displaying the 8th index of the array
    System.out.println("The 8th index of the array is " + arr[8] );
}
catch(ArrayIndexOutOfBoundsException excptn)
{
    System.out.println("Inside the catch block of ArrayIndexOutOfBoundsException");
    excptn.printStackTrace();
}
}
} 

Output:

Exception Handling Program In Java

Explanation: This time also the statement that is responsible for raising the ArrayIndexOutOfBoundsException has been put inside a try block. The raised exception is then handled in the catch block.

Errors

Errors are not exceptions. Errors are those problems that are out of the reach of the developers. Errors are not given that much importance because one can hardly do anything about them. Generally, a program can never recover from an error. In other words, errors are not recoverable. Errors occur when there are severe failures. A few of the errors generated by Java environments are VirtualMachineError, OutOfMemoryError, AsserstionError, etc.



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