[Easy-to-understand explanation! ] How to use Java instance

1. Prior knowledge

-[Latest] How to build Java environment on Ubuntu

Or

-[Even beginners can do it! ] How to create a Java environment on Windows 10 (JDK14.0.1)

As prior knowledge, the contents of the above link are required.

2. What is an instance?

--The entity (object) created based on the class is called instance. --Creating an object based on a class is called instantiation. -- Instance can be created by using new operator from a class when calling (using) a variable or method of another class. --The constructor is called when the instance is created.

3. What is a constructor?

--Constructor is a method that is executed when a class is instantiated, and is mainly used when initializing member variables of that class. --If there is no description of the constructor, default constructor is called. --The default constructor is a constructor that is empty (no processing) with no arguments.

4. Basic writing

Basic writing

public class main class name{
    public static void main(String[] args) {
        //Instance generation
Class name Variable name=new class name();    
    }
}
 
class class name{
    //Constructor (executed when instantiating)
name of the class(){
Initialization process, etc.
    }
}

--Basic instance creation is described as above.

5. Description example

Test.java

//Instance and constructor test classes
public class Test {
	//main method
	public static void main(String[] args) {
	    //instance(object)Generate a(Constructor call)
		Hello hello = new Hello();
	}
}

//Instance test class
class Hello {
  //constructor
  Hello() {
	  //Hello display
	  System.out.print("Hello");
  }
}

--Copy the above statement, specify S-JIS as the character code, save the file name as Test.java, and execute it at the command prompt. ↓ ↓

6. Special description example

Test1.java

//Instantiation in constructor
public class Test1 {
	//main method
	public static void main(String[] args) {
	    //instance(object)Generate a(Constructor call)
		new Hello1();
	}
}

//Constructor test class
class Hello1 {
  //constructor
  Hello1() {
      //instance(object)Generate a
      InstanceHello ih = new InstanceHello();
      //Instance method invocation
      ih.showHello();
  }
}

//Instance test class
class InstanceHello {
  //Hello display method
  void showHello(){
      System.out.print("Hello");
  }
}

Test2.java

//Instances not stored in variables
public class Test2 {
    //main method
    public static void main(String[] args) {
        //instance(object)Generate a&Method call
    	new Hello2().showHello();
    }
}

//Instance test class
class Hello2 {
  //Hello display method
  void showHello(){
      //Hello display
      System.out.print("Hello");
  }
}

--Copy the above statement, specify S-JIS as the character code, save the file name as Test1.java, Test2.java, and execute it at the command prompt. ↓ ↓

7. Related

-[Latest] How to build Java environment on Ubuntu -[Even beginners can do it! ] How to create a Java environment on Windows 10 (JDK14.0.1) -[Even beginners can do it! ] How to install Eclipse on Windows 10 (Java environment construction)