Java学习笔记（18）-对象数组

package day04;

import java.util.Arrays;

/*
 * 对象数组：元素是对象（元素是对象的引用）的数组
 */
public class Demo05 {
	public static void main(String[] args) {
		Point[] ary;//声明了数组变量ary
		ary = new Point[3];//创建了数组对象new Point[3]
		//new Point[3]实际情况：{null,null,null}
		//元素自动初始化为null,并不创建元素对象！
		System.out.println(ary[1]);//null
		ary[0] = new Point(3,4);
		ary[1] = new Point(5,6);
		ary[2] = new Point(1,2);
		System.out.println(ary[2]);//调用了对象的toString()
		System.out.println(ary[2].toString());
		System.out.println(Arrays.toString(ary));
		ary = new Point[]{new Point(1,2),new Point(6,7)};
		Point[] ary2 = {new Point(1,2),new Point(6,7)};
		System.out.println(Arrays.toString(ary));
		System.out.println(Arrays.toString(ary2));
	}
}

package day04;

public class Point/*extends Object*/ {
	private int x;
	private int y;
	public Point(){
		//无参数构造方法
	}
	public Point(int x,int y){
		this.x = x;
		this.y = y;
		//有参数构造器
		//构造器重载
	}
	public int getX(){
		return x;
	}
	public int getY(){
		return y;
	}
	//Point.java
	//toString是Object类定义，子类继承的方法
	//在打印对象时候，默认调用，重写这个方法可以打印的更好看！
	public String toString(){
		return "("+x+","+y+")";
	}
}

package day04;
/*
 * 二维数组
 * Java中没有真正的二维数组！Java二维数组是元素是数组的一维数组。元素是数组的数组。
 */
public class Demo06 {
	public static void main(String[] args) {
		int[][] ary = new int[2][3];//等价{{0，0，0}，{0，0，0}}
		ary[1] = new int[]{4,5,6,7};
		System.out.println(ary[1][2]);
		System.out.println(ary.length);
		System.out.println(ary[0].length);
		System.out.println(ary[1].length);
		
		for(int i=0;i