What is the method

A method is a set of code that organizes code blocks with separate functions into a whole and has special functions.

Be careful:

• The method must be created before it can be used, and the process becomes the definition of the method
• The method is not created to run directly and needs to be used manually before execution. This process is called method invocation

Definition and invocation of methods

1. Method Definition

• Format:

public static void Method Name(){
		//Method Body
	}

2. Method calls:

• Format:

Method Name();

Note: Method must be defined before calling, otherwise the program will error
For example:

public static void main(String[] args) {
		// Call to method
		isEvenNumber();
	}

The results are:

Example:

// Requirements: Define a method in which a variable is defined to determine if the number is even
	public static void isEvenNumber() {
		int number = 10;
		// Determine if it is even
		if (number % 2 == 0) {
			System.out.println(true);
		} else {
			System.out.println(false);
		}
	}
	public static void main(String[] args) {
		// Call to method
		isEvenNumber();
	}

• Method Exercise
  Requirement: Design a larger number for printing two numbers

	int a = 10;// Define two variables
	int b = 20;
	if (a > b) {// Branch statements handle variable size relationships
		System.out.println(a);
	} else {
		System.out.println(b);
	}
}

public static void main(String[] args) {
	getMax();
}

Definition and invocation of methods with parameters

1. Method definition with parameters

Format:

public static void Method Name(Data type variable name){//Single parameter
   	//Method Body
   }
   public static void Method Name(Data type variable name 1, data type variable name 2,......){//Multiple parameters
   	//Method Body
   }

Example:

public static void isEvenNumber(int number){//Single parameter
   	//Method Body
   }
   public static void getMax(int number1,int number2，......){//Multiple parameters
   	//Method Body
   }

Be careful:

• When a method is defined, neither the data type nor the variable name in the parameter can be missing, and any program that is missing will fail
• When defining a method, commas (,) are used to separate multiple parameters

2. Method calls with parameters
Format:

Method Name(Variable Name/constant value);//Single parameter
 Method Name(Variable Name 1/Constant value 1, variable name 2/Constant value 2,......);//Multiple parameters

Example:

isEvenNumber(5);//Single parameter
getMax(5，6);//Multiple parameters

Be careful:

• When a method is called, the number and type of parameters must match the settings in the method definition or the program will fail

Examples include:

 	public static void isEvenNumber(int number) {
		if (number % 2 == 0) {
			System.out.println(true);
		} else {
			System.out.println(false);
		}
	}

	public static void main(String[] args) {
		// Invocation of Constant Value
		isEvenNumber(10);
		// Call of variable
		int number = 10;
		isEvenNumber(number);
	}

Run result:

3. Formal and actual parameters

Parameter: The parameter in the method definition, which is equivalent to the variable definition format, for example, int number
Arguments: Parameters in a method call, equivalent to using variables or constants, for example: 10,number

Example:

//Design a method to print a larger number of two numbers from the method parameters
	public static void getMax(int a,int b) {//Define a method
		if (a > b) {// Branch statements handle variable size relationships
			System.out.println(a);
		} else {
			System.out.println(b);
		}
	}
	public static void main(String[] args) {
		//Direct Transfer Constant
		//When calling a method, you can give just a few, any type you want, any type you want
		//getMax(30);
		//getMax(10.0,20.0);
		getMax(10,20);
		//Define variables, pass
		int a=10;
		int b=20;
		getMax(a,b);
	}

Run result:

Definition and invocation of methods with return values

1. Method definition with return value

Format:

public static Data type method name(parameter){
   	return Data;
   }

Example 1:

public static boolean isEvenNummber(int number){
   	return true；
   }

Example 2:

public static int getMax(int a,int b){
   	return 100；
   }

Be careful:

• When defining a method, the return value after return matches the data type on the method definition, otherwise the program will fail

2. Method calls with return values
Format 1:

Method Name(parameter);

Example 1:

isEvenNumber(5);//Single parameter

Format 2:

Data type variable name=Method Name(parameter);

Example 2:

boolean flag=isEvenNumber(5);

Be careful:

• The return value of a method is usually received with a variable, otherwise it will be meaningless
  Example:
  Requirements: Defines a method that receives a parameter, determines whether the data is even, and returns true and false values

 //Defines a method that receives a parameter, determines whether the data is even, and returns true and false values
	public static boolean isEvenNumber(int number) {
		if (number % 2 == 0) {
			return true;
		} else {
			return false;
		}
	}

	public static void main(String[] args) {
		//1. Method name (parameter);
		System.out.println(isEvenNumber(10));
		//2. Data type variable name = method name (parameter);
		boolean flag=isEvenNumber(10);
		System.out.println(flag);

	}

Run result:

• Method Exercise with Return Value
  Requirements: Design a method to get a larger value of two numbers from parameters

//Requirements: Design a method to get a larger value of two numbers from parameters
	public static int getMax(int a,int b) {
		if (a > b) {// Branch statements handle variable size relationships
			return a;
		} else {
			return b;
		}
	}
	
	public static void main(String[] args) {
		int result=getMax(10,20);
		System.out.println(result);
//		//2. Print results directly
//		System.out.println(getMax(10,20));

Run result:

Notes on Methods

1. Method cannot nest definitions

//Correct code:
public static void methodOne() {
		//Snippet 1
	}
	public static void methodTwo() {
		//Code Snippet 2
	}
//Error code:	
public static void methodOne() {
		//Snippet 1
		public static void methodTwo() {
			//Code Snippet 2
		}
	}

2. void means no return value, return can be omitted or written separately without data

//Correct code 1:
	public static void methodOne() {
		//Snippet 1	
	}
//Correct code 2:
	public static void methodOne() {
		//Snippet 1
		return;
	}
//Error code:
	public static void methodOne() {
		//Snippet 1	
		return 100;
	}

General format for methods

Format:

public static Return value type method name(parameter){
   	Method Body;
   	return Data;
   }

• public static - modifier

• Return Value Type - The data type of the data returned after the method operation is complete; If the method operation is complete and there is no data return, void is written here and return is not typically written in the body of the method

• Method Name - Handle ID used when calling a method

• Parameters - consisting of data types and variable names separated by commas

• Method Body - Code Block to Complete Function

• Return - If the method operation is complete, returned from the data, used to return the data to the caller

• When defining the way, two clarities should be noted
  Explicit return value type: Mainly clarify whether there is data return after the method operation is completed, and if not, write void; If so, write the corresponding data type
  Explicit parameters: mainly clarify the type and number of parameters

• When calling a method
  A method of type void, called directly
  Non-void type method, variable is recommended for receiving calls