题目要求

1.定义一个Person类

属性：String name, boolean gender, int age, int id ,所有的变量必须为私有(private)。
无参构造函数:Person(), 功能：打印This is constructor 。
有参构造函数:Person(name, gender, age) ，功能：给属性赋值。
建议：使用Eclipse自动生成toString方法

2.定义类的初始化块

为Person类加入初始化块，在初始化块中对id属性赋值，并且要保证每次的值比上次创建的对象的值+1。然后在下一行打印This is initialization block, id is ... 其中...是id的值。
提示：可为Person类定义一个static属性来记录所创建的对象个数。

3.编写静态初始化块

打印This is static initialization block

4.编写main方法

首先输入n，代表要创建的对象数量。
然后从控制台分别读取n行的name, gender, age, 并调用有参构造函数Person(name, age, gender)新建对象。
将创建好的n个对象逆序输出(即输出toString()方法)。
使用无参构造函数新建一个Person对象，然后直接打印该对象。

思考

初始化类与对象有几种方法，构造函数、初始化块、静态初始化块。这三种方法执行的先后顺序是什么？各执行几次。

输入样例:

3
a 11 false
b 12 true
c 10 false

输出样例:

This is static initialization block
This is initialization block, id is 0
This is initialization block, id is 1
This is initialization block, id is 2
Person [name=c, age=10, gender=false, id=2]
Person [name=b, age=12, gender=true, id=1]
Person [name=a, age=11, gender=false, id=0]
This is initialization block, id is 3
This is constructor
null,0,false,3
Person [name=null, age=0, gender=false, id=3]

代码示例：


import java.util.*;

class Person{
    private String name;
    private int age;
    private boolean gender;
    private int id;
    private static int num=0;
    //初始化块
    static {
        System.out.println("This is static initialization block");
    }
    public Person(){
    	id=num;
        num++;
        System.out.println("This is initialization block, id is "+id);
        System.out.println("This is constructor");
        System.out.println(name+","+age+","+gender+","+id);
    }
    public Person(String name,int age,boolean gender){
    	id=num;
        num++;
        System.out.println("This is initialization block, id is "+id);
        this.name = name;
        this.age = age;
        this.gender = gender;
    }
    
    public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public boolean isGender() {
		return gender;
	}
	public void setGender(boolean gender) {
		this.gender = gender;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", gender=" + gender + ", id=" + id + "]";
	}
}
public class Main{
	public static void main(String []args){
        Scanner in = new Scanner(System.in);
        int n=in.nextInt();
        Person a[] = new Person[n];
        for(int i=0;i<n;i++){
        	String name = in.next();
        	int age = in.nextInt();
        	boolean gender = in.nextBoolean();
        	a[i] = new Person(name,age,gender);
        }
        for(int i=n-1;i>=0;i--) {
        	System.out.println(a[i].toString());
        }
        Person b = new Person();
        System.out.println(b);
    }
}