Method declaration in Java

Introduction

Methods help you organize your code into small, reusable actions. They make your program easier to read and use.

When you want to repeat a task many times without rewriting code.

When you want to break a big problem into smaller, manageable parts.

When you want to give a name to a set of instructions for clarity.

When you want to reuse code in different places of your program.

When you want to make your program easier to test and fix.

Syntax

Java

accessModifier returnType methodName(parameterList) {
    // method body
}

accessModifier controls who can use the method (like public or private).

returnType is the type of value the method gives back, or void if it returns nothing.

Examples

A method that prints a greeting and returns nothing.

Java

public void sayHello() {
    System.out.println("Hello!");
}

A method that adds two numbers and returns the result.

Java

private int add(int a, int b) {
    return a + b;
}

A method that checks if a number is even and returns true or false.

Java

public boolean isEven(int number) {
    return number % 2 == 0;
}

Sample Program

This program has two methods: one to greet the user and one to add two numbers. The main method calls them to show how methods work.

Java

public class Main {
    public static void main(String[] args) {
        greetUser();
        int sum = addNumbers(5, 7);
        System.out.println("Sum: " + sum);
    }

    public static void greetUser() {
        System.out.println("Welcome to the program!");
    }

    public static int addNumbers(int x, int y) {
        return x + y;
    }
}

Important Notes

Method names usually start with a lowercase letter and use camelCase.

Parameters inside parentheses are inputs the method needs to work.

Use return to send a value back from the method.

Summary

Methods group code into reusable blocks with a name.

They can take inputs (parameters) and give back outputs (return values).

Declaring methods helps keep your code clean and organized.

Practice

1. What is the correct way to declare a method in Java that returns an integer and takes no parameters?

easy

A. int getNumber { return 5; }

B. public int getNumber() { return 5; }

C. public getNumber() int { return 5; }

D. public int getNumber[] { return 5; }

Solution

1. Step 1: Check method signature format

   The correct method declaration includes access modifier, return type, method name, and parentheses for parameters.

2. Step 2: Validate syntax correctness

   public int getNumber() { return 5; } correctly uses 'public int getNumber()' with parentheses and a return statement.

3. Final Answer:

   public int getNumber() { return 5; } -> Option B

4. Quick Check:

   Method declaration = public int getNumber() { ... } [OK]

Hint: Method declaration needs return type, name, and parentheses [OK]

Common Mistakes:

• Omitting parentheses after method name
• Missing return type before method name
• Using brackets [] instead of parentheses for parameters

2. Which of the following is a correct method declaration syntax in Java?

easy

A. void printMessage(String message) { System.out.println(message); }

B. void printMessage(String message); { System.out.println(message); }

C. void printMessage String message { System.out.println(message); }

D. void printMessage(String message) System.out.println(message);

Solution

1. Step 1: Identify correct method header and body syntax

   Method header must have parentheses around parameters and body enclosed in braces.

2. Step 2: Check for syntax errors

   void printMessage(String message) { System.out.println(message); } correctly declares method with parameters in parentheses and body in braces.

3. Final Answer:

   void printMessage(String message) { System.out.println(message); } -> Option A

4. Quick Check:

   Method syntax = returnType name(params) { body } [OK]

Hint: Method parameters must be inside parentheses and body inside braces [OK]

Common Mistakes:

• Adding semicolon after method header
• Missing parentheses around parameters
• Omitting braces for method body

3. What will be the output of the following code?

public class Test {
  public static int add(int a, int b) {
    return a + b;
  }
  public static void main(String[] args) {
    System.out.println(add(3, 4));
  }
}

medium

A. 0

B. 34

C. 7

D. Error

Solution

1. Step 1: Understand method call and parameters

   The method add takes two integers and returns their sum.

2. Step 2: Calculate the return value

   Calling add(3, 4) returns 3 + 4 = 7, which is printed.

3. Final Answer:

   7 -> Option C

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Method add returns sum; 3 + 4 = 7 [OK]

Common Mistakes:

• Confusing concatenation with addition
• Expecting compile error due to static method
• Ignoring return value and expecting no output

4. Identify the error in the following method declaration:

public int multiply(int x, int y)
  return x * y;
}

medium

A. Extra semicolon after return statement

B. Missing return type

C. Incorrect parameter types

D. Missing opening brace '{' after method header

Solution

1. Step 1: Check method header and body braces

   The method header must be followed by an opening brace '{' to start the method body.

2. Step 2: Identify missing brace

   The code lacks '{' after the method header, causing a syntax error.

3. Final Answer:

   Missing opening brace '{' after method header -> Option D

4. Quick Check:

   Method body must start with '{' [OK]

Hint: Method body always starts with '{' after header [OK]

Common Mistakes:

• Forgetting opening brace '{'
• Placing return statement outside method body
• Confusing semicolon placement

5. You want to declare a method named filterPositive that takes an array of integers and returns a new array containing only the positive numbers. Which method declaration is correct?

hard

A. public int[] filterPositive(int[] numbers) { /* implementation */ }

B. public int filterPositive(int numbers[]) { /* implementation */ }

C. public void filterPositive(int[] numbers) { /* implementation */ }

D. public int filterPositive(int[] numbers[]) { /* implementation */ }

Solution

1. Step 1: Determine return type and parameter type

   The method returns an array of integers, so return type must be int[]. The parameter is an int array.

2. Step 2: Check syntax correctness

   public int[] filterPositive(int[] numbers) { /* implementation */ } correctly declares return type as int[] and parameter as int[]. Other options have wrong return types or parameter syntax.

3. Final Answer:

   public int[] filterPositive(int[] numbers) { /* implementation */ } -> Option A

4. Quick Check:

   Return type matches output array type [OK]

Hint: Return type must match method output type (int[] for array) [OK]

Common Mistakes:

• Using int instead of int[] as return type
• Incorrect parameter array syntax
• Using void when method returns data