24、使用 Java 官方教程学习：① 类变量和类方法详解；② 深入介绍 main() 方法

public class Child {
    public static int childCnt = 0;
    private String name;
    /**
     * 返回全部的孩子个数
     */
    public int getChildCnt() {
        return childCnt;
    }
    public Child(String name) {
        this.name = name;
        childCnt++;
        System.out.println("【" + this.name + "】小朋友加入了游戏");
    }
}

public class ChildPlaySnowman {
    public static void main(String[] args) {
        System.out.println();
        
        Child qy = new Child("庆医");
        Child hn = new Child("浩男");
        Child ms = new Child("莫松");
        Child wf = new Child("王凡");
        Child lh = new Child("陆昊");
        System.out.println();
        System.out.println("共有 " + qy.getChildCnt() + " 个小孩在玩游戏！");
        System.out.println("共有 " + Child.childCnt + " 个小孩在玩游戏！");
        System.out.println("共有 " + hn.childCnt + " 个小孩在玩游戏！");
    }
}

class MethodAccessDemo {
    public static int staticVar = 666;
    private String instanceVar = "庆医";
    public int instanceMethod1() {
        // instanceVar = 庆医
        System.out.println("instanceVar = " + instanceVar);
        // staticVar = 666
        System.out.println("staticVar = " + staticVar);
        // instanceMethod2()
        instanceMethod2();
        // staticMethod()
        staticMethod();
        return staticVar;
    }
    private static void staticMethod() {
        System.out.println("staticMethod()");
    }
    public void instanceMethod2() {
        System.out.println("instanceMethod2()");
    }
}
public class Demo {
    public static void main(String[] args) {
        MethodAccessDemo instance = new MethodAccessDemo();
        int cnt = instance.instanceMethod1();
        // staticVar = 666
        System.out.println("staticVar = " + cnt);
    }
}

/**
 * 捐款者
 */
class Donor {
    private static double totalMoney;
    private String name;
    public Donor(String name) {
        this.name = name;
    }
    public void donate(double val) {
        if (val <= 0) {
            System.out.println("金额必须大于0");
            return;
        }
        System.out.println("\n感谢【" + name + "】资助 " + val + " 元");
        totalMoney += val;
    }
    public static double getTotalMoney() {
        return totalMoney;
    }
}
public class Demo {
    public static void main(String[] args) {
        Donor wf = new Donor("王凡");
        wf.donate(10000);
        Donor zhn = new Donor("张浩男");
        zhn.donate(99999);
        Donor qy = new Donor("庆医");
        qy.donate(800);
        // 总共收到捐款金额：110799.0
        System.out.println("\n总共收到捐款金额：" + Donor.getTotalMoney());
    }
}

public class Demo {
    static int count;
    public void count() {
        System.out.println("count = " + (count++));
    }
    public static void main(String[] args) {
        // count = 0
        new Demo().count();
        // count = 1
        new Demo().count();
        // 2
        System.out.println(Demo.count);
    }
}

class Person {
    private int id;
    private static int total;
    public static int getTotalPerson() {
    /*
      1.id 是实例变量
      2.getTotalPerson() 是静态方法
      3.静态方法中不能够直接访问实例成员
     */
        // id++; // ERROR
        return total;
    }
    public Person() {
    /*
      1.total 类变量
      2.Person() 是构造方法, 构造方法是和实例相关的
      3.在构造方法中可以直接访问类变量
     */
        total++;
        id = total;
    }
}
public class TestPerson {
    public static void main(String[] args) {
        // total = 0
        System.out.println("total = " + Person.getTotalPerson());
    /*
      创建 Person 对象会调用构造方法, 构造方法的调用会使得 total 的值
      变为1, id 的值也变为1
     */
        new Person();
        // total = 1
        System.out.println("total = " + Person.getTotalPerson());
    }
}

class Person {
    private int id;
    public static int total;
    public static void setTotalPerson(int total) {
    /*
        1.setTotalPerson() 是类方法
      2.类方法中坚决不能使用 this 关键字
     */
        // this.total = total; // ERROR
        Person.total = total;
    }
    public Person() {
        total++;
        id = total;
    }
}
public class TestPerson {
    public static void main(String[] args) {
        Person.setTotalPerson(1);
        new Person();
        // 2
        System.out.println(Person.total);
    }
}

public class HelloWorld {
    public static void main(String[] args) {
        // Hello World!
        System.out.println("Hello World!");
    }
}

public class HelloWorld {
    public static void main(String[] args) {
        for (int i = 0; i < args.length; i++) {
            System.out.println("parameter" + (i + 1) + ": " + args[i]);
        }
    }
}

public class HelloWorld {
    public static void main(String[] canShu) { 
        for (int i = 0; i < canShu.length; i++) {
            System.out.println("parameter" + (i + 1) + ": " + canShu[i]);
        }
    }
}