7-5 jmu-Java-03面向对象基础-02-构造函数与初始化块 (20分)

1.定义一个Person类

属性：name(String)、gender（boolean)、age(int)、id(int) ，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]

import java.util.Scanner;

class Person {
	private String name;
	private int age;
	private boolean gender;
	private int id = num;
	private static int num = 0;

	public Person() {
		System.out.println("This is constructor ");
	}

	public Person(String name, int age, boolean gender) {
		this.name = name;
		this.gender = gender;
		this.age = age;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public boolean getGender() {
		return gender;
	}

	public void setGender(boolean gender) {
		this.gender = gender;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	{
		num++;
		System.out.println("This is initialization block, id is " + id);
	}
	

	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", gender=" + gender + ", id=" + id + "]";
	}

}

public class Main {
	static {
		System.out.println("This is static initialization block");
	}
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		Person p[] = new Person[n];
		for (int i = 0; i < p.length; i++) {
			String a = in.next();
			int b = in.nextInt();
			boolean c = in.nextBoolean();
			p[i] = new Person(a, b, c);

		}
		for (int i = n - 1; i >= 0; i--) {
			System.out.println(p[i]);
		}
		Person p1 = new Person();
		System.out.println(p1.getName() + "," + p1.getAge() + "," + p1.getGender() + "," + p1.getId());
		System.out.println(p1);

	}

}