已Mydate為例：

package text1;

public class MyDate {
	int year;
	int month;
	int day;
	
	//1.建構函式
	public MyDate(int y,int m,int d)
	{
		year = y;
		month = m;
		day = d;
	}
	
	//2.預設建構函式
	public MyDate()
	{/*
		year =  2018;
		month = 11;
		day = 11;
	*/
		this(2018,11,13);//在構造方法中，this必須是第一行語句
	}
	
	//建構函式過載
	       
	//4拷貝建構函式
	public MyDate(MyDate d)
	{
		//year =  d.year;
		//month = d.month;
		//day = d.day; 
		this(d.year,d.month,d.day);
	}
	
	//解構函式
	public void finalize()
	{
		System.out.println("空間已釋放！");
	}
	
	//String函式，輸出類物件
	public String toString()
	{
		return year + "年" + month + "月" + day + "日";
	}

    //判斷該類的兩個物件是否相等只能用equals()方法；
	//java不支援運算子過載，對於=、!=只能判斷兩個物件是否引用同一個例項
	public boolean equals(MyDate d)
	{
		return this==d || d!=null && this.year==d.year && this.month==d.month && this.day==d.day;
		//this表呼叫當前方法的物件；對於this.year，this.month，this.day中this可省略；
		//this==d判斷是否指向同一例項
	}
	
	public static void main(String arg[]) {
		
		MyDate d1 = new MyDate(2018,11,10);
		System.out.println(d1.toString());
		//d1.finalize();
		
		MyDate d2 = new MyDate();
		System.out.println(d2.toString());
		//d2.finalize();
		
		MyDate d3 = new MyDate(d2);
		System.out.println(d3.toString());
		//d3.finalize();
		
		//System.gc();//釋放所有垃圾

        System.out.println("d1與d2是否為同一天:  " + d1.equals(d2));
		System.out.println("d2與d3是否為同一天 : " + d2.equals(d3));
	}
	
}