List Collections sort

package gather;

import java.util.ArrayList;
import java.util.Collections;


public class CollecSortTest {

    public static void main(String[] args) {
        
        
//        System.out.println(list.isEmpty()); 判断结合是否为空
        
        ArrayList<String> list1   = new ArrayList<>(); 
        
        Collections.sort(list1); //方法1
        
        
        list1.add("222");
        list1.add("1");
        list1.add("444");
        list1.add("33");
//        list1.sort(new ComparatorOne());  //方法2
        
        Collections.sort(list1, ( first, second) -> first.length() - second.length());//  方法5 lambda表达式
        
         
        ArrayList<Student> list2   = new ArrayList<>(); 
        Student student1 = new Student();
        student1.setAge(1);
        
        Student student2 = new Student();
        student2.setAge(2);
        
        Student student3 = new Student();
        student3.setAge(3);
        
        list2.add(student3);
        list2.add(student2);
        list2.add(student1);
//        list2.sort(new ComparatorTwo()); //方法3
        
        Collections.sort(list2, ( first, second) -> second.getAge() - first.getAge());//  方法5 lambda表达式
        
        System.out.println("true"); 
        
    }
}

 

package gather;

import java.util.Comparator;

public class ComparatorOne implements Comparator<String> {

    @Override
    public int compare(String arg0, String arg1) {
        System.out.println("---ComparatorOne---"); 
        return arg0.length() - arg1.length();
    } 

}

package gather;

import java.util.Comparator;

public class ComparatorTwo implements Comparator<Student>{

    @Override
    public int compare(Student o1, Student o2) {
        
        System.out.println("---ComparatorTwo---"); 
        return o1.getAge()-o2.getAge();
    }
    
    

}