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Types of Errors in Java

Java is one of the most widely used programming languages in the world, and is known for its reliability and portability. However, like any other programming language, Java is not without its challenges. Programmers, especially beginners, often make mistakes in the development process. These errors can range from simple types to complex logic issues. In this section, we will explore types of errors in Java and how to solve them.

Let's explore some common types of errors in Java with example and their corresponding output. Here are the code snippets for each type of error:

Syntax Errors

Syntax errors are probably the easiest errors to spot. It occurs when code violates the rules of the Java programming language. These errors do not even compile the code. Common syntax errors include:

  1. Missing Semicolons: Java uses semicolons to separate statements. Omitting a semicolon at the end of a line can result in a syntax error.
  2. Mismatched Braces: Each opening curly brace '{' should be matched with a closing curly brace '}'. An imbalance between them will lead to a syntax error.
  3. Misspelled Keywords: If we misspell a Java keyword or use it in the wrong context, the code will not compile.

Syntax Error Example

File Name:

Output: error: ';' expected
        int x = 5
                 ^ error: cannot find symbol
        System.out.println("Hello, World!");

Syntax Error Explanation: In this code, there's a missing semicolon after the statement int x = 5, which results in a syntax error.

Runtime Errors

Runtime errors, also known as exceptions, occur during program execution. These errors can hinder rule execution and, if not handled properly, often lead to program termination. Common runtime errors include:

  1. Null Pointer Exception: It occurs when we attempt to access an object or invoke a method on an object that is null.
  2. ArrayIndexOutOfBounds Exception: It is raised when we try to access an array element using an index that is out of bounds.
  3. Arithmetic Exception: When attempting to divide by zero or perform an operation that's mathematically invalid, this exception is thrown.

Runtime Error Example

File Name:


Exception in thread "main" java.lang.ArithmeticException: / by zero
    at RuntimeErrorExample.main(

Runtime Error Explanation: In this code, we attempt to divide by zero, which leads to an ArithmeticException during runtime.

Logical Errors

Finding logical errors is the hardest because the code compiles without problems, and the program runs as expected. But the output is not what we want to do because of incorrect logic in the code. Identifying and correcting these errors often requires careful debugging and code analysis.

  1. Off-by-one Errors: These occur when loops or array indices are incremented or decremented incorrectly, leading to unintended behavior.
  2. Incomplete Conditionals: Failing to account for all possible cases in conditional statements can lead to logical errors.
  3. Incorrect Algorithm Implementation: If we use an incorrect algorithm to solve a problem, the program may produce incorrect results.

Logical Error Example

File Name:


The sum of the numbers from 1 to 5 is: 15

Logical Error Explanation: In this code, there is an off-by-one error. The loop should run from 1 to 5, but the condition i <= 5 should be i < 5 to get the correct sum.

Type Errors

  1. Type errors occur when we attempt to use variables, objects, or methods in ways that are incompatible with their data types. Common type errors include:
    1. Type Casting Issues: Incompatible type casting, such as casting an object of one class to another class that is not related, can result in type errors.
    2. Data Type Mismatch: Using variables or values of different data types in operations without proper conversion can lead to type errors.

Type Error Example

File Name:

Output: error: bad operand types for binary operator '+'
        int result = number + text; // Type mismatch
  first type:  int
  second type: String

Semantic Errors

Semantic errors are subtle mistakes that result from the misuse of linguistic concepts. Identifying them can be difficult and often requires a deep understanding of how the code is meant to be.

  1. Incorrect API Usage: Using a library or framework incorrectly can lead to semantic errors.
  2. Misunderstanding Object States: Not correctly managing the state of objects can lead to unexpected behavior.

Semantic Error Example

File Name:


The sum of a and b is: 15

Semantic Error Explanation: In this code, there's a semantic error where multiplication is used instead of addition to calculate the sum.

These examples demonstrate different types of errors in Java, and the output shows how they are identified and reported, either at compile-time or runtime. It's essential to understand and fix these errors to create correct and reliable Java programs.


In the world of Java programming, errors are an inevitable part of the development process. Understanding the different types of errors, such as syntax errors, runtime errors, logical errors, type errors, and semantic errors, is essential for debugging and maintaining code effectively. Through thorough testing, careful code review, and a solid understanding of Java best practices, developers can minimize and resolve these errors to create more robust and reliable Java applications.

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