父类：
public class Father {private double money=100;public double getMoney() {return money;}public void setMoney(double money) {this.money = money;}public void usePhone(){System.out.println("使用老年机");}
}

子类：有继承关系，并且重写父类的方法userPhone()
public class Children extends Father {public void usePhone(){System.out.println("继承money:"+getMoney()+"使用智能机");}
}

public class Test {public static void main(String[] args) {Father f=new Children(); //父类的引用指向子类对象。f.usePhone();//其实是调用子类的方法，输出：“继承money:100.0使用智能机”
    }
}

public class User {private Long id;private String name;private int age;public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}
}

public class User {private Long id;private String name;private String age; //改为String类型public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getAge() {return age;}public void setAge(int age) {this.age = String.valueOf(age);}
}

public class User {private Long id;private String name;private int age;public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {if(age>150){System.out.println("年龄不符合要求");//输出提示信息}else {this.age = age;}}
}

好处3：例如性别我们在数据库中一般都是已1、0方式来存储的，但是在前台我们又不能展示1、0，这里我们只需要在getter()方法里面做一些转换即可。

public class User {private Long id;private String name;private Integer sex;private String sexString;public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSexString() {if(sex==1){setSexString("男");}else if(sex==0){setSexString("女");}else {setSexString("未知");}return sexString;}public void setSexString(String sexString) {this.sexString = sexString;}
}