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Built-in Exceptions in Java with examples

Last Updated : 03 Jul, 2024
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Types of Exceptions in Java Built-in exceptions are the exceptions that are available in Java libraries. These exceptions are suitable to explain certain error situations. Below is the list of important built-in exceptions in Java. 

Examples of Built-in Exception:

1. Arithmetic exception : It is thrown when an exceptional condition has occurred in an arithmetic operation. 

Java 
// Java program to demonstrate 
// ArithmeticException
class ArithmeticException_Demo {
    public static void main(String[] args) {
        try {
            int a = 30, b = 0;
            int c = a / b; // cannot divide by zero
            System.out.println("Result = " + c);
        } catch (ArithmeticException e) {
            System.out.println("Can't divide a number by 0");
        }
    }
}

Output
Can't divide a number by 0

2. ArrayIndexOutOfBounds Exception: It is thrown to indicate that an array has been accessed with an illegal index. The index is either negative or greater than or equal to the size of the array. 

Java 
// Java program to demonstrate 
// ArrayIndexOutOfBoundException
class ArrayIndexOutOfBound_Demo {
    public static void main(String[] args) {
        try {
            int[] a = new int[5];
            a[5] = 9; // accessing 6th element in an array of
                      // size 5
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Array Index is Out Of Bounds");
        }
    }
}

Output
Array Index is Out Of Bounds


3. ClassNotFoundException : This Exception is raised when we try to access a class whose definition is not found. 

Java 
// Java program to illustrate the 
// concept of ClassNotFoundException
class Bishal {

} 

class Geeks {

}

class MyClass {
    public static void main(String[] args) {
        try {
            Object o = Class.forName(args[0]).newInstance();
            System.out.println("Class created for " + o.getClass().getName());
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {
            System.out.println("Exception occurred: " + e.getMessage());
        }
    }
}

Output:

ClassNotFoundException

4. FileNotFoundException : This Exception is raised when a file is not accessible or does not open. 

Java 
// Java program to demonstrate 
// FileNotFoundException
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;

class File_notFound_Demo {
    public static void main(String[] args) {
        try {
            // Following file does not exist
            File file = new File("file.txt");
            FileReader fr = new FileReader(file);
        } catch (FileNotFoundException e) {
            System.out.println("File does not exist");
        }
    }
}

Output
File does not exist

5. IOException : It is thrown when an input-output operation failed or interrupted 

JAVA 
// Java program to illustrate IOException
import java.io.*;

class Geeks {
    public static void main(String[] args) {
        try {
            FileInputStream f = new FileInputStream("abc.txt");
            int i;
            while ((i = f.read()) != -1) {
                System.out.print((char)i);
            }
            f.close();
        } catch (IOException e) {
            System.out.println("IOException occurred: " + e.getMessage());
        }
    }
}

Output:

error: unreported exception IOException; must be caught or declared to be thrown

6. InterruptedException : It is thrown when a thread is waiting, sleeping, or doing some processing, and it is interrupted. 

JAVA 
// Java Program to illustrate 
// InterruptedException
class Geeks {
public static void main(String args[])
    {
        Thread t = new Thread();
        t.sleep(10000);
    }
}

Output:

error: unreported exception InterruptedException; must be caught or declared to be thrown

7. NoSuchMethodException : t is thrown when accessing a method which is not found. 

JAVA 
// Java Program to illustrate 
// NoSuchMethodException
class Geeks {
    public Geeks() {
        try {
            Class<?> i = Class.forName("java.lang.String");
            try {
                i.getMethod("someMethod", Class[].class);
            } catch (SecurityException | NoSuchMethodException e) {
                e.printStackTrace();
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        new Geeks();
    }
}
}

Output:

error: exception NoSuchMethodException is never thrown 
in body of corresponding try statement

8. NullPointerException : This exception is raised when referring to the members of a null object. Null represents nothing 

JAVA 
// Java program to demonstrate NullPointerException
class NullPointer_Demo {
    public static void main(String[] args) {
        try {
            String a = null; // null value
            System.out.println(a.charAt(0));
        } catch (NullPointerException e) {
            System.out.println("NullPointerException..");
        }
    }
}

Output:

NullPointerException..

9. NumberFormatException : This exception is raised when a method could not convert a string into a numeric format. 

JAVA 
// Java program to demonstrate 
// NumberFormatException
class NumberFormat_Demo {
    public static void main(String[] args) {
        try {
            // "akki" is not a number
            int num = Integer.parseInt("akki");
            System.out.println(num);
        } catch (NumberFormatException e) {
            System.out.println("Number format exception");
        }
    }
}

Output:

Number format exception

10. StringIndexOutOfBoundsException : It is thrown by String class methods to indicate that an index is either negative than the size of the string. 

JAVA 
// Java program to demonstrate 
// StringIndexOutOfBoundsException
class StringIndexOutOfBound_Demo {
    public static void main(String[] args) {
        try {
            String a = "This is like chipping "; // length is 22
            char c = a.charAt(24); // accessing 25th element
            System.out.println(c);
        } catch (StringIndexOutOfBoundsException e) {
            System.out.println("StringIndexOutOfBoundsException");
        }
    }
}

Output:

StringIndexOutOfBoundsException

Some other important Exceptions

1. ClassCastException 

JAVA 
// Java Program to illustrate
// ClassCastException
class Test {
    public static void main(String[] args) {
        String s = "Geeks";
        Object o = s;
        try {
            String s1 = (String) new Object();
        } catch (ClassCastException e) {
            System.out.println("ClassCastException occurred: " + e.getMessage());
        }
    }
}

Output:

Exception in thread "main" java.lang.ClassCastException: 
java.lang.Object cannot be cast to java.lang.String

2. StackOverflowError 

JAVA 
// Java Program to illustrate 
// StackOverflowError
class Test {
public static void main(String[] args)
    {
        m1();
    }
public static void m1()
    {
        m2();
    }
public static void m2()
    {
        m1();
    }
}

Output:

Exception in thread "main" java.lang.StackOverflowError

3. NoClassDefFoundError 

JAVA 
public class NoClassDefFoundErrorExample {
    public static void main(String[] args) {
        try {
            // Trying to create an instance of a class that doesn't exist
            MyNonExistentClass obj = new MyNonExistentClass();
        } catch (NoClassDefFoundError e) {
            System.out.println("NoClassDefFoundError occurred: " + e.getMessage());
        }
    }
}

Output:

Note: If the corresponding Test.class file is not found 
during compilation then we will get Run-time Exception
saying Exception in thread "main" java.lang.NoClassDefFoundError

4. ExceptionInInitializerError 

Code 1: 

JAVA 
// Java Program to illustrate 
// ExceptionInInitializerError
class Test {
    static int x = 10 / 0;
public static void main(String[] args)
    {
    }
}

Output:

Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.ArithmeticException: / by zero

Code 2 : 

JAVA 
// Java Program to illustrate 
// ExceptionInInitializerError
class Test {
    static
    {
        String s = null;
        System.out.println(s.length());
    }
public static void main(String[] args)
    {
    }
}

Output:

Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.NullPointerException

Explanation : The above exception occurs whenever while executing static variable assignment and static block if any Exception occurs.

5. IllegalArgumentException 

JAVA 
// Java Program to illustrate 
// IllegalArgumentException
class Test {
public static void main(String[] args)
    {
        Thread t = new Thread();
        Thread t1 = new Thread();
        t.setPriority(7); // Correct
        t1.setPriority(17); // Exception
    }
}

Output:

Exception in thread "main" java.lang.IllegalArgumentException

Explanation:The Exception occurs explicitly either by the programmer or by API developer to indicate that a method has been invoked with Illegal Argument.

6. IllegalThreadStateException 

JAVA 
// Java Program to illustrate 
// IllegalStateException
class Test {
public static void main(String[] args)
    {
        Thread t = new Thread();
        t.start();
        t.start();
    }
}

Output:

Exception in thread "main" java.lang.IllegalThreadStateException

Explanation : The above exception rises explicitly either by programmer or by API developer to indicate that a method has been invoked at wrong time.

7. AssertionError 

JAVA 
// Java Program to illustrate 
// AssertionError
class Test {
    public static void main(String[] args) {
        int x = 5;
        // If x is not greater than or equal to 10
        // then we will get the AssertionError
        assert (x >= 10) : "x is less than 10";
    }
}

Output:

Exception in thread "main" java.lang.AssertionError

Explanation : The above exception rises explicitly by the programmer or by API developer to indicate that assert statement fails.

IllegalArgumentException: This exception is thrown when an illegal argument is passed to a method.

For example:

Java 
public class IllegalArgumentExceptionExample {
    public static void main(String[] args) {
        try {
            // Trying to pass an invalid argument to a method
            calculateArea(-5.0);
        } catch (IllegalArgumentException e) {
            System.out.println("IllegalArgumentException occurred: " + e.getMessage());
        }
    }

    public static void calculateArea(double radius) {
        if (radius < 0) {
            // Throwing an IllegalArgumentException with a custom message
            throw new IllegalArgumentException("Radius cannot be negative");
        }
        double area = Math.PI * radius * radius;
        System.out.println("Area: " + area);
    }
}

Output
IllegalArgumentException occurred: Radius cannot be negative

FileNotFoundException: This exception is thrown when a file cannot be found.

For example:

Java 
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

public class FileNotFoundExceptionExample {
    public static void main(String[] args) {
        try {
            // Trying to read a file that doesn't exist
            readFile("non-existent-file.txt");
        } catch (FileNotFoundException e) {
            System.out.println("FileNotFoundException occurred: " + e.getMessage());
        } catch (IOException e) {
            System.out.println("IOException occurred: " + e.getMessage());
        }
    }

    public static void readFile(String fileName) throws FileNotFoundException, IOException {
        File file = new File(fileName);
        FileInputStream fis = new FileInputStream(file);

        // Read the contents of the file
        byte[] buffer = new byte[1024];
        int bytesRead;
        while ((bytesRead = fis.read(buffer)) != -1) {
            // Process the read bytes
            System.out.println("Read " + bytesRead + " bytes.");
        }

        fis.close();
    }
}

Output
FileNotFoundException occurred: non-existent-file.txt (No such file or directory)


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Built-in Exceptions in Java with examples

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Bishal Kumar Dubey
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