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

 1 class first
 2 {
 3     public static void main(String[] args){
 4         int[] array;
 5         array = new int[5];
 6         for(int i=0;i<5;i++){
 7             array[i]=i;
 8         }
 9         for(int i=4;i>=0;i--){
10             System.out.println(array[i]);
11         }
12     }
13 }

3.简单的类:class

 1 class first
 2 {
 3     public static void main(String[] args){
 4         Human Person = new Human() ;
 5         Person.age();
 6         System.out.println(Person.height);
 7     }
 8 }
 9 class Human
10 {
11     void age(){
12         System.out.println("I am 12");
13     }
14     int height = 10;
15 }

4.构造函数

 1 class first
 2 {
 3     public static void main(String[] args){
 4         Human Person = new Human(180) ;
 5         Person.age();
 6         System.out.println(Person.height);
 7     }
 8 }
 9 class Human
10 {
11     public Human(int h){
12         this.height =h;
13         System.out.println("I am SmarTop");
14     }
15     void age(){
16         System.out.println("I am 12");
17     }
18     int height = 10;
19 }

5.重载

 1 class first
 2 {
 3     public static void main(String[] args){
 4         Human Person = new Human(180,"SmarTop") ;
 5         Person.age();
 6         System.out.println(Person.height);
 7     }
 8 }
 9 class Human
10 {
11     public Human(int h){
12         this.height =h;
13         System.out.println("I am SmarTop");
14     }
15     Human(int h , String name){
16         this.height = h;
17         this.name = name;
18         System.out.println("Name:"+name+"
Height:"+h);
19     }
20     void age(){
21         System.out.println("I am 2");
22     }
23     int height = 10;
24     String name;
25 }

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;
}