Java 方法覆盖

方法覆盖示例：

public class OverrideTest01{
    public static void main(String[] args){
        //ChinaPeople cp = new ChinaPeople("张三");  //错误: 子类无法继承父类的构造方法；
        ChinaPeople cp = new ChinaPeople();
        cp.setName("张三");
        cp.speak();
        
        AmericPeople ap = new AmericPeople();
        ap.setName("tom");
        ap.speak();
    }
}

class People{
    String name;      //实例属性
    
    public People(){      //构造方法
        
    }
    public People(String name){
        this.name = name;
    }
    
    //setter and getter
    public void setName(String name){
        this.name = name;
    }
    public String getName(){
        return this.name;
    }
    
    public void speak(){
        System.out.println(name + " .....");
    }
}

class ChinaPeople extends People{
    public void speak(){    //重写父类的speak方法
        System.out.println(this.getName() + "正在说汉语。");
    }
}

class AmericPeople extends People{
    public void speak(){
        System.out.println(this.getName() + " is speaking.");
    }
}

 重写Object类中的toString()方法：

public class OverrideTest02{
    public static void main(String[] args){
        MyDate md = new MyDate();
        System.out.println(md.toString());  //MyDate@512ddf17，默认输出对象在堆中的内存地址
        System.out.println(md);  //MyDate@512ddf17，对象后不带toString()输出结果一样，默认输出对象在堆中的内存地址
        
        MyDate md1 = new MyDate();    //重写toString()方法后，“对象.toString()” 可以输出符合要求的年月日格式； 
        System.out.println(md1.toString());
        System.out.println(md1);
    }
}

class MyDate{       //MyDate类默认继承Object类，所以会默认继承Object类的toString()方法
    private int year;
    private int month;
    private int day;
    
    public MyDate(){
        this(1970,1,1);
    }
    public MyDate(int year, int month, int day){
        this.year = year;
        this.month = month;
        this.day = day;
    }
    
    public void setYear(int year){
        this.year = year;
    }
    public int getYear(){
        return year;
    }
    public void setMonth(int month){
        this.month = month;
    }
    public int getMonth(){
        return month;
    }
    public void setDay(int day){
        this.day = day;
    }
    public int getDay(){
        return day;
    }
    
    public String toString(){      //重写Object类中的toString方法
        return year + "年" + month + "月" + day + "日";
    }
    
}