Method declaration in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a method declaration in Java?

A method declaration defines a block of code that performs a specific task. It includes the method's name, return type, parameters (if any), and the body with statements to execute.

beginner

Identify the parts of this method declaration:

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

Parts:
- public: access modifier
- int: return type
- add: method name
- (int a, int b): parameters
- { return a + b; }: method body

beginner

What does the return type in a method declaration specify?

It specifies the type of value the method will send back to the caller. If the method does not return a value, the return type is void.

beginner

True or False: A method declaration must always have parameters.

False. A method can have zero or more parameters. Parameters are optional depending on what the method needs to do.

beginner

What is the purpose of the method body in a method declaration?

The method body contains the code statements that define what the method does when it is called.

Which part of a method declaration specifies the method's name?

A The method body

B The access modifier

C The parameter list

D The identifier after the return type

The method name is the identifier that comes right after the return type in the declaration.

What keyword is used when a method does not return any value?

A null

B void

C none

D empty

The keyword void indicates the method returns no value.

Which of these is a valid method declaration in Java?

A public int calculateSum(int a, int b) { return a + b; }

B int calculateSum(a, b) { return a + b; }

C public calculateSum(int a, int b) { return a + b; }

D public int calculateSum(int a, int b)

Option A has correct syntax with access modifier, return type, method name, parameters, and body.

Can a method have no parameters?

A Yes, parameters are optional

B No, parameters are required

C Only if the return type is void

D Only if the method is static

Methods can have zero or more parameters depending on their purpose.

What does the method body contain?

A The method's name

B The return type

C The code statements to execute

D The parameter list

The method body contains the instructions that run when the method is called.

Explain the components of a Java method declaration and their roles.

Think about what each part tells the program about the method.

Describe how you would declare a method that returns no value and takes no parameters.

Remember the keyword for no return value and how to write empty parentheses.

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