25. Errors in Java

 

Errors in Java

• An error defines a reasonable issue that is topping the proper execution of the program.
• Programming errors often remains undetected until the program is compiled or executed.
• Errors should be removed from compiling and executing.
• In Java, an Error is a subclass of Throwable class.

Types of Errors

Generally, there are 3 types of errors which are as:

Compile-Time or Syntax Error

• These are those errors which prevent the code from running because of incorrect syntax.
• These errors are detected by the compiler and an error message is displayed onto the screen while displaying.

class CompileTimeError {

    public static void main(String[] arr) {

        int a = 4 // No semicolon

        int b;

        b = 2.5;// Declared variable type and initialize variable type are different

        c = 8; // Variable data-type not declared

       

        System.out.println(a + d); // Variable d not declared

    // Missing parenthesis

}

Output :

CompileTimeError.java:3: error: ';' expected
int a = 4 // No semicolon
            ^
1 error

Run-Time Errors or Exceptions

• These are detected during the execution of the program.
• During compilation, the compiler has no technique to detect these kinds of errors.
• Sometimes, these are discovered when the user enters an invalid data or data which is not relevant.
• It occurs when user asks the computer to do something that the computer is unable to reliably do.

import java.util.Scanner;

class RunTimeError {

    public static void main(String[] arr) {

        Scanner input = new Scanner(System.in);

        System.out.print("Enter a number for dividing 1625: ");

        int num = input.nextInt();

        System.out.println("Integer part of 1625 dividing by " + num + " is: " + 1625 / num);

        input.close();

        System.out.println("Success...");

    }

}

Output :

Enter a number for dividing 1625: 65
Integer part of 1625 dividing by 65 is: 25
Success...

Exception in thread "main" java.lang.ArithmeticException: / by zero
          at RunTimeError.main(RunTimeError.java:20)

Logical or Semantic Error

• When our program compiles and executes, but executes some different output.
• These errors are neither detected by compiler nor by the JVM.
• These errors are caused due to an incorrect idea or concept used by the programmer while coding.

class LogicalError {

    public static void main(String[] arr) {

        int a = 1234, rev = 0;

        System.out.println("Reversing a number...");

        while (a != 0) {

            rev = rev * 10 + a / 10; // rev = rev*10 + a%10

            a = a / 10;

        }

        System.out.println("The reverse of 1234 is " + rev);

    }

}

Output :

Reversing a number...
The reverse of 1234 is 124210

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