JAVA笔记4__static关键字/对象数组/foreach/方法的可变参数

/**
 * static关键字：修饰属性（实质就是全局变量）、方法（无需本类的对象即可调用此方法）、类。
 * 1.static方法只能调用static方法
 * 2.static方法只能访问static数据
 * 3.static方法不能以任何方式引用this或super
 */
public class Main {
    public static void main(String[] args) {
        A a = new A();  a.val = 2;
        A a1 = new A(); a1.val = 3;
        System.out.println(a.val+" "+a1.val);
        B b = new B();  b.val = 2;
        B b1 = new B(); b1.val = 3;
        System.out.println(b.val+" "+b1.val); //b和b1拥有同一份val
        A.say();
    }
}

class A{
    int val = 1;
    public static void say(){
        System.out.println("Hello~~");
    }
}
class B{
    static int val = 1; //静态数据不属于对象，属于类
}

 

import java.lang.String;
import java.util.Arrays;
import java.util.Scanner;

/**
 * 对象数组
 */
public class Main {
    public static void main(String[] args) {
        MonkeyManager  mm = new MonkeyManager();
        mm.add(new Monkey("1"));
        mm.add(new Monkey("2"));
        mm.add(new Monkey("2"));
        mm.add(new Monkey("4"));
        mm.delete("2");
        mm.list();
        
        Monkey temp1 = new Monkey("1");
        mm.update(temp1);
        mm.list();
    }
}

class MonkeyManager{
    private Monkey[] ms = new Monkey[3];
    private int count = 0;
    public void add(Monkey m){
        if(count<ms.length){
            ms[count++] = m;
            System.out.println("Successful add monkey: "+m.name);
        }
        else{
            System.out.print("空间已满！进行扩充...."); 
            int newLen = (ms.length*3)/2+1;
            ms = Arrays.copyOf(ms, newLen);
            System.out.println("扩充后的长度为："+newLen);
            ms[count++] = m;
            System.out.println("Successful add monkey: "+m.name);
        }
    }
    public void list(){
        for(int i=0;i<count;++i) ms[i].say();
    }
    public void delete(String name){
        boolean flag = true;
        while(flag){
            flag = false;
            for(int i=0;i<count;++i) if(ms[i].name.equals(name)){
                for(int j=i;j<count-1;++j) ms[j]=ms[j+1];
                ms[count-1] = null;
                --count;
                System.out.println("Successful delete monkey: "+name);
                flag = true;
                break;
            }
        }
    }
    public Monkey find(String name){
        for(int i=0;i<count;++i) if(ms[i].name.equals(name)) return ms[i];
        return null;
    }
    public void update(Monkey m){
        Monkey s = find(m.name);
        if(s!=null){
            s.name = "helloWorld";
        }
    }
}
class Monkey{
    String name;
    public Monkey(String name){
        this.name = name;
    }
    public void say(){
        System.out.println("I'm "+name);
    }
}

 

public class Main {
    public static void main(String[] args) {
        /**
         * foreach语法
         * for(类型 变量名：数组或集合){ //输出操作 }
         */
        String[] names = {"1","2","3","4"};
        for(String i:names) System.out.println(i);
        
        
        /**
        * 方法的可变参数
        * 1.只能有一个
        * 2.有多个参数时，可变参数放在最后
        */
        method1(names);
        method2(123,"a1","a2","a3");
        method2(123,names);
    }
    public static void method1(String[] na){
        for(String i:na) System.out.println(i);
    }
    public static void method2(int x,String... na){ //参数为可变参数(只能有一个)
        System.out.println("x="+x);
        for(String i:na) System.out.println(i);
    }
}