Built-in Exceptions in Java with examples

Types of Exceptions in Java Built-in exceptions are the exceptions which 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[6] = 9; // accessing 7th 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)
    {
        Object o = class.forName(args[0]).newInstance();
        System.out.println("Class created for" + o.getClass().getName());
    }
}

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("E:// 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[])
    {
        FileInputStream f = null;
        f = new FileInputStream("abc.txt");
        int i;
        while ((i = f.read()) != -1) {
            System.out.print((char)i);
        }
        f.close();
    }
}

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()
    {
        Class i;
        try {
            i = Class.forName("java.lang.String");
            try {
                Class[] p = new Class[5];
            }
            catch (SecurityException e) {
                e.printStackTrace();
            }
            catch (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 = new String("Geeks");
        Object o = (Object)s;
        Object o1 = new Object();
        String s1 = (String)o1;
    }
}

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

// Java Program to illustrate
// NoClassDefFoundError
class Test //
    {
public static void main(String[] args)
    {
        System.out.println("HELLO GEEKS");
    }
}

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)
    {
        // If x is not greater than or equal to 10
        // then we will get the run-time exception
        assert(x >= 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 void setAge(int age) {
    if (age < 0 || age > 120) {
        throw new IllegalArgumentException("Invalid age");
    }
    this.age = age;
}

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

Java

try {
    FileReader reader = new FileReader("file.txt"); // throws FileNotFoundException
} catch (FileNotFoundException e) {
    System.out.println("File not found");
}

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