Java初学几个程序背诵

1.Hello world

class first
{
    public static void main(String[] args){
        System.out.println("Hello world");
    }
}

2.数组 -> for循环

class first
{
    public static void main(String[] args){
        int[] array;
        array = new int[5];
        for(int i=0;i<5;i++){
            array[i]=i;
        }
        for(int i=4;i>=0;i--){
            System.out.println(array[i]);
        }
    }
}

3.简单的类:class

class first
{
    public static void main(String[] args){
        Human Person = new Human() ;
        Person.age();
        System.out.println(Person.height);
    }
}
class Human
{
    void age(){
        System.out.println("I am 12");
    }
    int height = 10;
}

 4.构造函数

class first
{
    public static void main(String[] args){
        Human Person = new Human(180) ;
        Person.age();
        System.out.println(Person.height);
    }
}
class Human
{
    public Human(int h){
        this.height =h;
        System.out.println("I am SmarTop");
    }
    void age(){
        System.out.println("I am 12");
    }
    int height = 10;
}

5.重载

class first
{
    public static void main(String[] args){
        Human Person = new Human(180,"SmarTop") ;
        Person.age();
        System.out.println(Person.height);
    }
}
class Human
{
    public Human(int h){
        this.height =h;
        System.out.println("I am SmarTop");
    }
    Human(int h , String name){
        this.height = h;
        this.name = name;
        System.out.println("Name:"+name+"
Height:"+h);
    }
    void age(){
        System.out.println("I am 2");
    }
    int height = 10;
    String name;
}

6.封装和接口

class two
{
    public static void main(String[] args){
        Human aPerson = new Human(160);
        System.out.println(aPerson.getHeight());
        aPerson.growHeight(170);
        System.out.println(aPerson.getHeight());
        aPerson.replaceBreath(100);
    }
}
class Human
{
    public Human(int h){
        this.height = h;
        System.out.println("I am born");
    }
    public int getHeight(){
        return this.height;
    }
    public void growHeight(int h){
        this.height = this.height + h;
    }
    private void breath(){
        System.out.println("I am nicia");
    }
    public void replaceBreath(int rep){
        int i;
        for(i=0;i<rep;i++){
            this.breath();
        }
    }
    private int height;
}