collection java 反序_java使用Collection.sort指定升序或降序的三种方法

第一种方法，Bean中实现Comparator接口:

public class CollectionsTest {

public static void main(String[] args) {

List list = new ArrayList();

//BeanClass 需实现Comparable接口

BeanClass bean1 = new BeanClass();

BeanClass bean2 = new BeanClass();

bean1.para = 1;

bean2.para = 2;

list.add(bean1;

list.add(bean2);

Collections.sort(list);

System.out.println(list.get(0).para);

System.out.println(list.get(1).para);

}

}

BeanClass类

public class BeanClass implements Comparable{

int para;

public int compareTo(BeanClass bc) {

// return this.para - bc.para; //升序

return bc.para-this.para; //降序

}

}

第二种方法，自定义比较器

public class CollectionsClass {

public static void main(String[] args) {

List list = new ArrayList();

BeanClass bean1 = new BeanClass();

BeanClass bean2 = new BeanClass();

bean1.para = 1;

bean2.para = 2;

list.add(bean1);

list.add(bean2);

Collections.sort(list,new MyComparator());

System.out.println(list.get(0).para);

System.out.println(list.get(1).para);

}

}

MyComparator类

public class MyComparator implements Comparator{

public int compare(BeanClass bean1, BeanClass bean2) {

//return bean1.para-bean2.para; //升序

return bean2.para-bean1.para; //降序

}

}

第三种，和第二种一样，不过使用匿名类

public class CollectionsClass {

public static void main(String[] args) {

List list = new ArrayList();

BeanClass bean1 = new BeanClass();

BeanClass bean2 = new BeanClass();

bean1.para = 1;

bean2.para = 2;

list.add(bean1);

list.add(bean2);

Collections.sort(list,new Comparator(){

@Override

public int compare(BeanClass o1, BeanClass o2) {

// return o1.para - o2.para; //升序

return o2.para - o1.para; //降序

}

});

System.out.println(list.get(0).para);

System.out.println(list.get(1).para);

}

}