Types of Error in Java

In Java, errors are problems that occur during the execution or compilation of a program. They can be broadly categorized into three main types:

1. Compile-time Errors

These errors occur when you try to compile the program — before it runs.
They are usually syntax or semantic errors detected by the Java compiler (javac).

Examples:

• Missing semicolon (;)
• Using an undeclared variable
• Misspelling a keyword
• Type mismatch

Example Code:

public class Example {
    public static void main(String[] args) {
        int a = 5
        System.out.println(a);
    }
}

Error: Missing semicolon (;) → Compile-time error

1. Runtime Errors

• These occur while the program is running, after successful compilation.
• They cause the program to crash or behave unexpectedly.

Examples:

• Dividing by zero → ArithmeticException
• Accessing invalid array index → ArrayIndexOutOfBoundsException
• Null object access → NullPointerException
• File not found → FileNotFoundException

Example Code:

public class Example {
    public static void main(String[] args) {
        int a = 10 / 0;
        System.out.println(a);
    }
}

Error: ArithmeticException: / by zero → Runtime error

1. Logical Errors

• These occur when the program runs successfully but produces the wrong output.
• The compiler and runtime won’t catch them — they are human mistakes in logic.

Examples:

• Using the wrong formula
• Incorrect loop conditions
• Wrong variable used in calculation

Example Code:

public class Example {
    public static void main(String[] args) {
        int a = 10, b = 5;
        System.out.println("Sum = " + (a - b)); // Logical mistake
    }
}

Output: Sum = 5 → Incorrect result due to logic error