在testO包中

// 主程序TestInterface.java 
package testO;

import testT.*;

public class TestInterface {

    public static void main(String[] args) {
        
        
        
        Students stu = new Students("学成餐");
        stu.eat();
        
        Teachers terche = new Teachers("教师餐");
        terche.eat();
        
        Parents parent = new Parents("家长餐");
        parent.eat();
        
        
        Car car = new Car();
        car.runTime(10.5, 3.0, 5.3);
        Plant plant = new Plant();
        plant.runTime(10.5,3.0,5.3);
        
    }

}

// 接口facePerson .java
package testO;

public interface facePerson {
    public String free = "免费";
    public void eat();
    public void sleep();
}

// Parents.java 类
package testO;

public class Parents implements facePerson{
    
    private String food;
    
    public Parents() {}
    public Parents(String food) {
        this.food = food;
    }
    @Override
    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("家长食堂:"+this.food);
    }

    @Override
    public void sleep() {
        // TODO Auto-generated method stub
        System.out.println("家长公寓");
    }
    public void setFood(String food) {
        this.food = food;
    }
    public String getFood() {
        return food;
    }

}

// 接口Students .java
package testO;

public class Students implements facePerson{
    
    private String food;

    
    public Students() {}
    public Students(String food) {
        this.food = food;
    }
    @Override
    public void eat() {
        // TODO Auto-generated method stub
        
        System.out.println("学生食堂:"+ this.food + facePerson.free);
    }

    @Override
    public void sleep() {
        // TODO Auto-generated method stub
        System.out.println("学生宿舍");
    }
    
    public void setFood(String food) {
        this.food = food;
    }
    public String getFood() {
        return food;
    }

}

// Teachers .java 类
package testO;

public class Teachers implements facePerson{
        
    private String food;
    
    public Teachers() {}
    public Teachers(String food) {
        
        this.food = food;
    }
    @Override
    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("教师食堂:"+this.food);
    }

    @Override
    public void sleep() {
        // TODO Auto-generated method stub
        System.out.println("教师公寓");
    }
    public void setFood(String food) {
        this.food = food;
    }
    public String getFood() {
        return food;
    }

}

在testT包中

// 接口 Computed.java
package testT;

public interface Computed {
    public void runTime(double a,double b,double c);
}

// 类 Car.java
package testT;

public class Car implements Computed{
    @Override
    public void runTime(double a, double b, double c) {
        // TODO Auto-generated method stub
        double time = a*b/c;
        System.out.println("car运行的时间："+ time);
    }
}
// 类 Plant.java
package testT;

public class Plant implements Computed{

    @Override
    public void runTime(double a, double b, double c) {
        // TODO Auto-generated method stub
        double time = (a+b)/c;
        System.out.println("Plant运行时间："+ time);
    }

}

运行的结果：

执行结果.png