TreeSet 排序

 

class Person1 implements Comparable <Person1>{
    private Float height;
    private String name;
    
    Person1(float height)
    {
        this.height=height;
    }

    public Float getHeight() {
        return height;
    }

    public void setHeight(float height) {
        this.height = height;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public int compareTo(Person1 p) {
        if(this.getHeight()<p.getHeight()){
            return 1;
            
        }else if(this.getHeight()>p.getHeight()){
            return -1;
        }else{
            return 0;    
        }
        
    }
}


public class Question3_1 {

    public static void main(String[] args) {
        Person1 p1=new Person1(23.4f);
        p1.setName("Stud1");
        Person1 p2=new Person1(2.34f);
        p2.setName("Stud2");
        Person1 p3=new Person1(34.32f);
        p3.setName("Stud3");
        Person1 p4=new Person1(56.45f);
        p4.setName("Stud4");
        Person1 p5=new Person1(21.4f);
        p5.setName("Stud5");
        
      
        TreeSet<Person1> al=new TreeSet<Person1>();
        al.add(p1);
        al.add(p2);
        al.add(p3);
        al.add(p4);
        al.add(p5);
        
       
        for(Person1 p:al)
            System.out.println(p.getName()+" "+p.getHeight());

    }

}

 

 

 

结果：

Stud4 56.45
Stud3 34.32
Stud1 23.4
Stud5 21.4
Stud2 2.34

TreeSet 中的对象时自定义对象时，需实现Comparable 接口

 

Exception in thread "main" java.lang.ClassCastException: com.cn.aug26.Person1 cannot be cast to java.lang.Comparable
    at java.util.TreeMap.compare(TreeMap.java:1188)
    at java.util.TreeMap.put(TreeMap.java:531)
    at java.util.TreeSet.add(TreeSet.java:255)
    at com.cn.aug26.Question3_1.main(Question3_1.java:64)