java---类充当属性

package com.javasm.obj;
public class StudentInfo {
    public int id;
    public String name;
    public String gender;
    //Computer类充当学生属性
    //能够解决空的问题，弊端：占据很多堆内存
    //public Computer computer = new Computer("DELL");//null
    public Computer computer;
    public void study() {
        //每个学生都使用自己的电脑上网学习
        //调用上网的方法  Computer.online();
        if(computer==null){
            System.out.println("computer can not is null");
            return;
        }
        computer.online(name);
    }
}
​

package com.javasm.obj;
public class Computer {
    public String brand;//电脑品牌名
​
    public void online(String studentName) {
        System.out.println(studentName + "正在使用" + brand + "学习。。。。");
    }
    public Computer() {
    }
    public Computer(String brand) {
        this.brand = brand;
    }
}

package com.javasm.test;
import com.javasm.obj.Computer;
import com.javasm.obj.StudentInfo;
public class StudentInfoTest {
    public static void main(String[] args) {
        StudentInfo studentInfo = new StudentInfo();
        studentInfo.id = 1001;
        studentInfo.name = "张三";
        studentInfo.gender = "男";
//        Computer myComputer = studentInfo.computer;
//        myComputer = new Computer("DELL");
//        studentInfo.computer = myComputer;
        studentInfo.computer = new Computer("DELL");
        studentInfo.study();
    }
}