java method

public static void sayHi(){
		System.out.println("Hi!");
	}

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

public static void sayHi(String name){
		System.out.println("Hi!" + name);
	}

	public static void main(String[] args){
		sayHi("Tom");
		sayHi("Bob");
	}

[vagrant@localhost java]$ javac MyApp.java
[vagrant@localhost java]$ java MyApp
Hi!Tom
Hi!Bob

public static String sayHi(String name){
		return "Hi!" + name;
	}

	public static void main(String[] args){
		String msg = sayHi("Steve");
		System.out.println(msg);
	}

[vagrant@localhost java]$ javac MyApp.java
[vagrant@localhost java]$ java MyApp
Hi!Steve

classを使ってみよう

class User {
	String name = "Me!";

	void sayHi(){
		System.out.println("hi!");
	}

}

public class MyApp {

	public static void main(String[] args){
		User tom;
		tom = new User();

		System.out.println(tom.name);
		tom.sayHi();
	}
}

[vagrant@localhost java]$ javac MyApp.java
[vagrant@localhost java]$ java MyApp
Me!
hi!

なるほど。

コンストラクタ

class User {
	String name;

	User(String name){
		this.name = name;
	}

	void sayHi(){
		System.out.println("hi!" + this.name);
	}

}

public class MyApp {

	public static void main(String[] args){
		User tom;
		tom = new User("Tom");

		System.out.println(tom.name);
		tom.sayHi();
	}
}

[vagrant@localhost java]$ javac MyApp.java
[vagrant@localhost java]$ java MyApp
Tom
hi!Tom

なるほど、何故か急に分かってきた。
classの継承

class User {
	String name;

	User(String name){
		this.name = name;
	}

	void sayHi(){
		System.out.println("hi!" + this.name);
	}
}

class AdminUser extends User {
	AdminUser(String name){
		super(name);
	}

	void sayHello(){
		System.out.println("hello!" + this.name);
	}	
}

public class MyApp {

	public static void main(String[] args){
		User tom = new User("Tom");
		System.out.println(tom.name);
		tom.sayHi();

		AdminUser bob = new AdminUser("bob");
		System.out.println(bob.name);
		bob.sayHi();
		bob.sayHello();
	}
}

@override 継承した時に親クラスのメソッドを使う

class User {
	String name;

	User(String name){
		this.name = name;
	}

	void sayHi(){
		System.out.println("hi!" + this.name);
	}
}

class AdminUser extends User {
	AdminUser(String name){
		super(name);
	}

	void sayHello(){
		System.out.println("hello!" + this.name);
	}
	@Override void sayHi(){
		System.out.println("[admin]hi!" + this.name);
	}	
}

public class MyApp {

	public static void main(String[] args){
		User tom = new User("Tom");
		System.out.println(tom.name);
		tom.sayHi();

		AdminUser bob = new AdminUser("bob");
		System.out.println(bob.name);
		bob.sayHi();
		bob.sayHello();
	}
}

[vagrant@localhost java]$ javac MyApp.java
[vagrant@localhost java]$ java MyApp
Tom
hi!Tom
bob
[admin]hi!bob
hello!bob
ほうほう