Object类及equals()方法

1 ==  对于基本数据类型，根据两端的值来判断是否相等，即使两端的数据类型不同，也可以返回true。引用数据类型，比较引用变量类型的地址是否相等

2 equals（）是比较引用类型变量是否相等，也是比较地址值

3 ctrl+shift+t 查看源码  ctrl+/ 注释

package lianxi2;

public class TestEquals {
    public static void main(String []args){
   Department d1 = new Department();
   Department d2 = new Department();
   System.out.println(d1 == d2);   //false
   System.out.println(d1.equals(d2)); //Object的equals方法 false
   
   String s1 = new String("tt");  
   String s2 = new String("tt");
   System.out.println(s1 == s2);   //false
   System.out.println(s1.equals(s2));  //String类重写equals方法 true
    }
}                                                                                                                                                  

package lianxi3;

public class TestMyDate {

    /**
     * @param args
     */
    public static void main(String[] args) {
        MyDate md1 = new MyDate(5,27,2014);
        MyDate md2 = new MyDate(5,27,2014);
        if(md1 == md2){               // md1!=md2
            System.out.println("md1==md2");
        }
        else{
            System.out.println("md1!=md2");
        }
        if(md1.equals(md2)){       //true
            System.out.println("true");
        }
        else{
            System.out.println("false");  
        }
    }
}
class MyDate{
    private int month;
    private int day;
    private int year;
    public MyDate(int month, int day, int year) {
        super();
        this.month = month;
        this.day = day;
        this.year = year;
    }
    public int getMonth() {
        return month;
    }
    public void setMonth(int month) {
        this.month = month;
    }
    public int getDay() {
        return day;
    }
    public void setDay(int day) {
        this.day = day;
    }
    public int getYear() {
        return year;
    }
    public void setYear(int year) {
        this.year = year;
    }
//    //手动创建equals
//    public boolean equals(Object obj){//体现多态性
//        if(this==obj){
//            return true;
//        }
//        else if(obj instanceof MyDate){
//            MyDate m = (MyDate)obj;
//            return this.day==m.day 
//            && this.month == m.month
//            && this.year == m.year;
//        }
//        return false;
//    }
    
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        MyDate other = (MyDate) obj;
        if (day != other.day)
            return false;
        if (month != other.month)
            return false;
        if (year != other.year)
            return false;
        return true;
    }
    
}