集合排序

ArrayList存放学生对象及排序

【问题描述】

编写一个学生类，包含姓名、学号、年龄、专业四个属性，并完善get /set方法、构造方法、toString()方法。

toString()方法参考如下：

public String toString() {

return "Student [name=" + name + ", id=" + id + ", age=" + age + ", major=" + major + "]";

}

有三位学生的信息，参考代码如下

Student s1=new Student("zhang",1401, 20, "computer");

Student s2=new Student("liu",1402,19,"law");

Student s3=new Student("wang",1403,17,"mechanical");

请完成以下内容：

1）创建一个ArrayList对象list，将上述三位学生加入到集合中，并遍历list，显示学生信息；

2）在学生 “liu”的前面插入一个学生，学生的信息如下：("li",1409,16,"english")
并再一次遍历list，确认学生“li”已经被正确插入。

3）根据学生的年龄，按照年龄从小到大的顺序对这4位学生进行排序，并再次遍历，显示学生信息。

package test;
//自定义排序
public class Student implements Comparable {//排序接口强制让学生具有比较性
    private String name;
    private int id;
    private int age;
    private String major;

    public Student(String name, int id, int age, String major) {
        super();
        this.name = name;
        this.id = id;
        this.age = age;
        this.major = major;
    }


    public int getAge() {
        return age;
    }


    public String toString() {

        return "Student [name=" + name + ", id=" + id + ", age=" + age + ", major=" + major + "]";

    }


    @Override
    public int compareTo(Object o) {
        Student s = (Student)o;
        return this.age-s.getAge();
    }
    

}

package test;

import java.util.*;

public class ArrayList1 {
    

    public static void main(String[] args) {
        List c = new ArrayList();
        Student s1=new Student("zhang",1401, 20, "computer");
        Student s2=new Student("liu",1402,19,"law");
        Student s3=new Student("wang",1403,17,"mechanical");
        c.add(s1);
        c.add(s2);
        c.add(s3);
        
//      Iterator it = c.iterator();//while遍历
//        while (it.hasNext()) {
//            Student s = it.next();
//            System.out.println(s);
//            System.out.println();
//        }
        for(Iterator iter = c.iterator();iter.hasNext();){
            Student s = iter.next();
            System.out.println(s);
            System.out.println();
        }
        
        Student s4=new Student("li",1409,16,"english");
        c.add(1,s4);
        
        Iterator it1 = c.iterator();
        while (it1.hasNext()) {
            Student s = it1.next();
            System.out.println(s);
            System.out.println();
        }
        
        
//        Collections.sort(c);                  //第一种排序内比较
//        Collections.sort(c,new Outcompare()); //第二种排序自定义比较器（外）
        Collections.sort(c,new Comparator(){//第三种排序匿名内部类

            /*@Override
            public int compare(Object o1, Object o2) {
                Student w1 = (Student)o1;//未加泛型强制转换
                Student w2 = (Student)o2;
                return w1.getAge()-w2.getAge();
            }*/

            @Override
            public int compare(Student o1, Student o2) {
                return o1.getAge()-o2.getAge();
            }});
        Iterator it2 = c.iterator();
        while (it2.hasNext()) {
            Student s = it2.next();
            System.out.println(s);
            System.out.println();
        }
        

        
        
    }
    
    
                                            
}
   
   

package test;

import java.util.Comparator;

public class Outcompare implements Comparator{//比较器

    @Override
    public int compare(Object o1, Object o2) {
        Student w1 = (Student)o1;
        Student w2 = (Student)o2;
        return w1.getAge()-w2.getAge();
    }

}