Java常用方法-集合工具类常用方法

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真香~

对象List按属性排序

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class Animal{
    private String kind;
    private int quantity;

    public Animal(String k,int q){
      this.kind = k;
      this.quantity = q;
    }
}


public class Main{

  public static void main(String[] args) {
    Animal dog = new Animal("狗",10000);
    Animal cat = new Animal("猫",5000);
    Animal pig = new Animal("猪",2000);

    List<Animal> animalList = new ArrayList<Animal>();
    animalList.add(dog);
    animalList.add(cat);
    animalList.add(pig);

    Collections.sort(animalList, new Comparator<TestA>() {
        @Override
        public int compare(TestA o1, TestA o2) {
            //升序
            return o1.getAge().compareTo(o2.getAge());
        }
    });

    Collections.sort(animalList, new Comparator<TestA>() {
        @Override
        public int compare(TestA o1, TestA o2) {
            //降序
            return o1.getAge().compareTo(o2.getAge());
        }
    });      

  }
}

List初始化时进行赋值

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List<Long> ids = Arrays.asList(98765432109L,12345678901L);