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Java – Top Exception and Error

February 28, 2017 SJ Exception Handling 0

In this article, we will discuss top exception and error in java with their description & examples

Top Exception in Java:

1. Null Pointer Exception

Exception Name :NullPointerException
Fully qualified name :java.lang.NullPointerException
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.RuntimeException
  • JVM raises NullPointerException, whenever operation is performed on null reference
  • For example, if we have an un-initialized String variable then trying to check or get its length using length() method throws/raises NullPointerException
  • See below example for reference

StringOperationForCheckingLength.java

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package in.bench.resources.top.exception.in.java;
 
public class StringOperationForCheckingLength {
 
    public static void main(String[] args) {
 
        // string variable
        String str = null;
 
        // checking length
        int len = str.length();
 
        // printing to console
        System.out.println("Length of str is : " + len);
    }
}

Output:

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Exception in thread "main" java.lang.NullPointerException
    at in.bench.resources.top.exception.in.java
    .StringOperationForCheckingLength.main(
            StringOperationForCheckingLength.java:11)

2. Array Index Out Of Bounds Exception

Exception Name :ArrayIndexOutOfBoundsException
Fully qualified name :java.lang.ArrayIndexOutOfBoundsException
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.IndexOutOfBoundsException, which is sub-class of java.lang.RuntimeException
  • JVM raises ArrayIndexOutOfBoundsException, whenever we are trying to perform operation like accessing or assigning an array element with out-of-range of index
  • That’s index is greater than length of an array or index with negative value
  • For example, if original length of an array is 5 then trying to assign/access a value at 7th index-position, raises/throws ArrayIndexOutOfBoundsException
  • See below example for reference

ArrayOperationOnInvalidIndex.java

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package in.bench.resources.top.exception.in.java;
 
public class ArrayOperationOnInvalidIndex {
 
    public static void main(String[] args) {
 
        // character array of length 5
        char[] ch = new char[5];
 
        // assigning value at 7th index-psotion
        ch[7] = 'B';
 
        // printing to console
        System.out.println("The value at 7th index-position is : " + ch[7]);
    }
}

Output:

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Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 7
    at in.bench.resources.top.exception.in.java
    .ArrayOperationOnInvalidIndex.main(
            ArrayOperationOnInvalidIndex.java:11)

3. Arithmetic Exception

Exception Name :ArithmeticException
Fully qualified name :java.lang.ArithmeticException
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.RuntimeException
  • JVM raises ArithmeticException, whenever we perform invalid arithmetic operation like divide by zero, which throws ArithmeticException with “divide by zero” as exception description
  • For example, performing a division with divisor as zero, throws/raises ArithmeticException as stated above
  • See below example for reference

DivideByZeroExample.java

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package in.bench.resources.top.exception.in.java;
 
public class DivideByZeroExample {
 
    public static void main(String[] args) {
 
        // performing division
        int quotient = 19/0;
 
        // printing to console
        System.out.println("The quotient after division is : " + quotient);
    }
}

Output:

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Exception in thread "main" java.lang.ArithmeticException: / by zero
    at in.bench.resources.top.exception.in.java.DivideByZeroExample
    .main(DivideByZeroExample.java:8)

4. Class Cast Exception

Exception Name :ClassCastException
Fully qualified name :java.lang.ClassCastException
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.RuntimeException
  • JVM raises ClassCastException, whenever we are trying to do invalid type-casting
  • That’s type-casting from super-class type to sub-class type, throws/raises ClassCastException at runtime (although compilation succeeds)
  • In simple words, when RHS Object doesn’t satisfy “IS-A” relationship with LHS, then this exception is raised
  • For example, assigning Object-type to String-type results in type-casting exception at runtime
  • See below example for reference

ClassCastExceptionExample.java

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package in.bench.resources.top.exception.in.java;
 
public class ClassCastExceptionExample {
 
    public static void main(String[] args) {
 
        // Object-type
        Object object = new Object();
 
        // assigning Object-type to String-type
        String str = (String) object;
 
        // printing to console
        System.out.println("String is : " + str);
    }
}

Output:

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Exception in thread "main" java.lang.ClassCastException:
java.lang.Object cannot be cast to java.lang.String
    at in.bench.resources.top.exception.in.java.ClassCastExceptionExample
    .main(ClassCastExceptionExample.java:11)

 

5. Illegal Argument Exception

Exception Name :IllegalArgumentException
Fully qualified name :java.lang.IllegalArgumentException
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.RuntimeException
  • IllegalArgumentException is raised because of passing wrong/invalid argument to a method
  • For example, setting Thread priority to more than integer value 10 or negative value results in this type of exception
  • Because valid range for Thread priority is 1 to 10
  • See below example for reference

InvalidArgumentForThreadPriority.java

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package in.bench.resources.top.exception.in.java;
 
public class InvalidArgumentForThreadPriority {
 
    public static void main(String[] args) {
 
        // create a new Thread
        Thread t = new Thread();
 
        // set wrong/invalid priority
        t.setPriority(11);
    }
}

Output:

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Exception in thread "main" java.lang.IllegalArgumentException
    at java.lang.Thread.setPriority(Unknown Source)
    at in.bench.resources.top.exception.in.java
    .InvalidArgumentForThreadPriority
    .main(InvalidArgumentForThreadPriority.java:11)

6. Number format Exception

Exception Name :NumberFormatException
Fully qualified name :java.lang.NumberFormatException
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.IllegalArgumentException, which is child-class of java.lang.RuntimeException
  • NumberFormatException is raised when we try to convert string to numeric value like integer, float, double, etc and string passed isn’t properly formatted
  • For example, if we pass numeric 10 as string to parseInt() method of Integer class, then it convert into numeric value 10
  • Whereas trying to convert string value of “ben” to integer, results in NumberFormatException
  • See below example for reference

ParseStringToInteger.java

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package in.bench.resources.top.exception.in.java;
 
public class ParseStringToInteger {
 
    public static void main(String[] args) {
 
        // VALID - trying to convert string into integer value
        int resultValid = Integer.parseInt("10");
        System.out.println("The Value is : " + resultValid);
 
        // INVALID - trying to convert string into integer value
        int resultInvalid = Integer.parseInt("ben");
        System.out.println("The Value is : " + resultInvalid);
    }
}

Output:

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The Value is : 10
Exception in thread "main" java.lang.NumberFormatException:
    For input string: "ben"
    at java.lang.NumberFormatException.forInputString(Unknown Source)
    at java.lang.Integer.parseInt(Unknown Source)
    at java.lang.Integer.parseInt(Unknown Source)
    at in.bench.resources.top.exception.in.java.ParseStringToInteger
    .main(ParseStringToInteger.java:12)

7. Illegal Thread State Exception

Exception Name :IllegalThreadStateException
Fully qualified name :java.lang.IllegalThreadStateException
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.IllegalArgumentException, which is child-class of java.lang.RuntimeException
  • IllegalThreadStateException is raised when we try to start the Thread again, when it is already in started state
  • For example, invoking start() method of Thread 2nd time results in IllegalThreadStateException
  • See below example for reference

StartingThreadAgain.java

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package in.bench.resources.top.exception.in.java;
 
public class StartingThreadAgain {
 
    public static void main(String[] args) {
 
        // create a new Thread
        Thread t = new Thread();
 
        // 1st time - starting Thread
        t.start();
 
        // 2nd time - starting Thread AGAIN
        t.start();
    }
}

Output:

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Exception in thread "main" java.lang.IllegalThreadStateException
    at java.lang.Thread.start(Unknown Source)
    at in.bench.resources.top.exception.in.java.StartingThreadAgain
    .main(StartingThreadAgain.java:14)

8. Interrupted Exception

Exception Name :InterruptedException
Fully qualified name :java.lang.InterruptedException
Exception Type :Checked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.Exception
  • Generally, this exception-type is encountered whenever we are working with threading or multi-threading programming
  • Being checked exception, it need to be handled either by try-catch block or declare exception using throws clause
  • Sleep() & join() method of Thread class & wait() method of Object class throw this exception
  • For example, invoking interrupt on a Thread which is in sleeping/waiting state results in throwing this exception-type
  • See below example for reference

InterruptingThread.java

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package in.bench.resources.top.exception.in.java;
 
public class InterruptingThread {
 
    public static void main(String[] args) {
 
        // create a new Thread
        Thread t = new Thread(){
 
            public void run() {
 
                try {
                    Thread.sleep(5000);
                }
                catch (InterruptedException iex) {
                    iex.printStackTrace();
                }
            }
        };
 
        // start a Thread
        t.start();
 
        // interrupt a Thread
        t.interrupt();
    }
}

Output:

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java.lang.InterruptedException: sleep interrupted
    at java.lang.Thread.sleep(Native Method)
    at in.bench.resources.top.exception.in.java.InterruptingThread$1
    .run(InterruptingThread.java:13)

9. File Not Found Exception

Exception Name :FileNotFoundException
Fully qualified name :java.io.FileNotFoundException
Exception Type :Checked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.io.IOException
  • Whenever we are working with file, then it is must to handle FileNotFoundException
  • Because sometime it is possible that accessing file location isn’t available or else file itself not available at the specified location
  • For example, trying to access a file from specified location but file isn’t available at that location
  • See below example for reference

FileProcessing.java

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package in.bench.resources.top.exception.in.java;
 
import java.io.FileNotFoundException;
import java.io.FileReader;
 
public class FileProcessing {
 
    public static void main(String[] args) throws FileNotFoundException {
 
        // performing IO operation
        // assumed that, we are trying to access file from remote location
        FileReader fileReader = new FileReader("D:/Folder/test.txt");
    }
}

Output:

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Exception in thread "main" java.io.FileNotFoundException:
D:\Folder\test.txt (The system cannot find the path specified)
    at java.io.FileInputStream.open(Native Method)
    at java.io.FileInputStream.<init>(Unknown Source)
    at java.io.FileInputStream.<init>(Unknown Source)
    at java.io.FileReader.<init>(Unknown Source)
    at in.bench.resources.top.exception.in.java.FileProcessing
    .main(FileProcessing.java:12)

10. SQL Exception

Exception Name :SQLException
Fully qualified name :java.lang.SQLException
Exception Type :Checked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.io.IOException
  • After loading driver file for respective database, whenever we perform any operation with database and supplied credentials or database table/columns is incorrect
  • Then this exception-type is raised
  • For example, passing wrong database URL for a non-existent database results in rising SQLException
  • See below example for reference

JdbcConnectionExample.java

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package in.bench.resources.top.exception.in.java;
 
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
 
public class JdbcConnectionExample {
 
    public static void main(String[] args) {
 
        // declare variables
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
 
        // Step 1: Loading or
        // registering Oracle JDBC driver class
        try {
            Class.forName("oracle.jdbc.driver.OracleDriver");
        }
        catch(ClassNotFoundException cnfex) {
            System.out.println(
                    "Problem in loading Oracle JDBC driver");
            cnfex.printStackTrace();
        }
 
        // Step 2: Opening database connection
        try {
 
            // Step 2.A: Create and
            // get connection using DriverManager class
            connection = DriverManager.getConnection(
                    "jdbc:oracle:thin:@localhost:1521:xe",
                    "scott",
                    "tiger");
 
            // Step 2.B: Creating JDBC Statement
            statement = connection.createStatement();
 
            // Step 2.C: Executing SQL and
            // retrieve data into ResultSet
        }
        catch(SQLException sqlex){
            sqlex.printStackTrace();
        }
        finally {
 
            // Step 3: Closing database connection
        }
    }
}

Output:

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java.sql.SQLException: Io exception:
    The Network Adapter could not establish the connection
    at oracle.jdbc.driver.DatabaseError.throwSqlException(
            DatabaseError.java:112)
    at oracle.jdbc.driver.DatabaseError.throwSqlException(
            DatabaseError.java:146)
    at oracle.jdbc.driver.DatabaseError.throwSqlException(
            DatabaseError.java:255)
    at oracle.jdbc.driver.T4CConnection.logon(
            T4CConnection.java:387)
    at oracle.jdbc.driver.PhysicalConnection.<init>(
            PhysicalConnection.java:414)
    at oracle.jdbc.driver.T4CConnection.<init>(
            T4CConnection.java:165)
    at oracle.jdbc.driver.T4CDriverExtension.getConnection(
            T4CDriverExtension.java:35)
    at oracle.jdbc.driver.OracleDriver.connect(
            OracleDriver.java:801)
    at java.sql.DriverManager.getConnection(
            Unknown Source)
    at java.sql.DriverManager.getConnection(
            Unknown Source)
    at in.bench.resources.top.exception.in.java.JdbcConnectionExample
    .main(JdbcConnectionExample.java:31)

11. Class Not Found Exception

Exception Name :ClassNotFoundException
Fully qualified name :java.lang.ClassNotFoundException
Exception Type :Checked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.Exception
  • Generally this exception raised, when we try to execute a program and required .class files is missing from class-path
  • For example, trying to load driver file for respective databases but it isn’t available at runtime
  • Possible reason for this type of exception is, executing a JDBC program without updating class-path with required JAR files
  • See below example for reference

JdbcConnectionExample.java

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package in.bench.resources.top.exception.in.java;
 
public class JdbcConnectionExample {
 
    public static void main(String[] args) {
 
        // declare variables
 
        // Step 1: Loading or registering Oracle JDBC driver class
        try {
            Class.forName("oracle.jdbc.driver.OracleDriver");
        }
        catch(ClassNotFoundException cnfex) {
            System.out.println("Problem in loading Oracle JDBC driver");
            cnfex.printStackTrace();
        }
 
        // Step 2: Opening database connection
    }
}

Output:

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java.lang.ClassNotFoundException: oracle.jdbc.driver.OracleDriver
Problem in loading Oracle JDBC driver
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Unknown Source)
    at in.bench.resources.top.exception.in.java.JdbcConnectionExample
.main(JdbcConnectionExample.java:11)

Top Error in Java:

12. No Class Def Found Error

Exception Name :NoClassDefFoundError
Fully qualified name :java.lang.NoClassDefFoundError
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.LinkageError, which is child-class of java.lang.Error
  • JVM raises NoClassDefFoundError, whenever we try to execute a program and required .class files is missing from class-path
  • Possible reason for this type of exception is, required file is present during compilation but missing while executing the same program
  • For example, below program exhibits “HAS-A” relationship & compilation succeeds whereas during program execution JVM unable to find required .class file
  • See below example for reference

SimilarException.java

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package in.bench.resources.top.exception.in.java;
 
public class SimilarException {
 
    // using below declared TestFile class
    static TestFile tf = new TestFile();
 
    public static void main(String[] args) {
 
        // invoke method
        tf.display();
    }
}
 
class TestFile {
 
    public void display() {
        System.out.println("Display message");
    }
}

Output:

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java.lang.NoClassDefFoundError:
    in/bench/resources/top/exception/in/java/TestFile
    at in.bench.resources.top.exception.in.java.SimilarException.<clinit>(
            SimilarException.java:6)
Caused by: java.lang.ClassNotFoundException:
    in.bench.resources.top.exception.in.java.TestFile
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 1 more
Exception in thread "main"

Q) Difference between ClassNotFoundException and NoClassDefFoundError ?

  • ClassNotFoundException occurs, when we try to execute a program and required .class file isn’t available at runtime. Also, there won’t be compile-time error as we are trying to load class using Class.forName(“fully.qualified.name”);
  • NoClassDefFoundError occurs, when we try to execute a program and required .class file isn’t available at runtime. Because required file was available during program compilation but missing while executing (for some reasons)
  • Read ClassNotFoundException v/s NoClassDefFoundError for more details

13. Exception in Initializer Error

Exception Name :ExceptionInInitializerError
Fully qualified name :java.lang.ExceptionInInitializerError
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.LinkageError, which is child-class of java.lang.Error
  • JVM raises ExceptionInInitializerError, whenever we try perform some assignment operation in static variable or inside static blocks
  • For example, printing length of a string variable inside static block where string variable is referencing to null reference, results in throwing ExceptionInInitializerError
  • See below example for reference

ExceptionErrorDemo.java

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package in.bench.resources.top.exception.in.java;
 
public class ExceptionErrorDemo {
 
    // static block
    static {
 
        String str = null;
        System.out.println("The length of string is : " + str.length());
    }
 
    // main() method - JVM execution start here
    public static void main(String[] args) {
    }
}

Output:

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java.lang.ExceptionInInitializerError
Caused by: java.lang.NullPointerException
    at in.bench.resources.top.exception.in.java.ExceptionErrorDemo.<clinit>(
            ExceptionErrorDemo.java:9)
Exception in thread "main"

14. Stack Overflow Error

Exception Name :StackOverflowError
Fully qualified name :java.lang.StackOverflowError
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.VirtualMachineError, which is child-class of java.lang.Error
  • JVM raises StackOverflowError, whenever we perform repeated recursive method call
  • See below example for reference

RecursiveDemo.java

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package in.bench.resources.top.exception.in.java;
 
public class RecursiveDemo {
 
    // main() method - JVM execution starts here
    public static void main(String[] args) {
 
        // invoking methodA
        methodA();
    }
 
    // method A - recursively invoking method B
    public static void methodA() {
 
        // invoking methodB
        methodB();
    }
 
    // method B - recursively invoking method A
    public static void methodB() {
 
        // invoking methodA
        methodA();
    }
}

Output:

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Exception in thread "main" java.lang.StackOverflowError
    at in.bench.resources.top.exception.in.java.RecursiveDemo
.methodA(RecursiveDemo.java:16)
    at in.bench.resources.top.exception.in.java.RecursiveDemo
.methodB(RecursiveDemo.java:23)
    at in.bench.resources.top.exception.in.java.RecursiveDemo
.methodA(RecursiveDemo.java:16)
    at in.bench.resources.top.exception.in.java.RecursiveDemo
.methodB(RecursiveDemo.java:23)
    at in.bench.resources.top.exception.in.java.RecursiveDemo
.methodA(RecursiveDemo.java:16)
    at in.bench.resources.top.exception.in.java.RecursiveDemo
.methodB(RecursiveDemo.java:23)
    at in.bench.resources.top.exception.in.java.RecursiveDemo
.methodA(RecursiveDemo.java:16)
    at in.bench.resources.top.exception.in.java.RecursiveDemo
.methodB(RecursiveDemo.java:23)
    at in.bench.resources.top.exception.in.java.RecursiveDemo
.methodA(RecursiveDemo.java:16)
    at in.bench.resources.top.exception.in.java.RecursiveDemo
.methodB(RecursiveDemo.java:23)
........
........
........
........

15. Assertion Error

Exception Name :AssertionError
Fully qualified name :java.lang.AssertionError
Exception Type :Unchecked Exception
Exception hierarchy : See below figure

Description:

  • It is the direct sub-class of java.lang.Error
  • Whenever we want to test our assumption, then JVM raises AssertionError if our assumption goes wrong (basically the other way of our assumption)
  • This is mainly used in JUnit for testing purpose
  • For example, in the below assertion test when user enters integer value less than 18 then our assumpotion fails
  • And then accordingly JVM raises AssertionError
  • Note: AssertionError can be thrown explicitly using throw keyword
  • See below example for reference

AssertionTest.java

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package in.bench.resources.top.exception.in.java;
 
import java.util.Scanner;
 
public class AssertionTest {
 
    public static void main(String[] args) {
 
        // for taking input from users
        Scanner scanner = new Scanner(System.in);
        System.out.print("Age for obtaning Driver License : ");
        int value = scanner.nextInt(); 
 
        // assertion test for Age
        assert value>=18 : "Age should be more than 18 years old";
    }
}

Output:

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Age for obtaning Driver License : 16
Exception in thread "main" java.lang.AssertionError:
Age should be more than 18 years old
    at in.bench.resources.top.exception.in.java.AssertionTest
.main(AssertionTest.java:15)

Related Articles:

References:

Happy Coding !!
Happy Learning !!

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