Collections.sort的两个方法

//Collections.sort(List<?> list) 调用系统Comparable中的compareTo方法进行升序排序
//Collections.sort(List<T> list,Comparator<? super T>) 根据指定比较器排序


import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class SortTest {



    public static void main(String[] args) {
        List<String> lists = new ArrayList<String>();
        List<A> list = new ArrayList<A>();
        List<B> listB = new ArrayList<B>();
        lists.add("5");
        lists.add("2");
        lists.add("9");
        //lists中的对象String 本身含有compareTo方法，所以可以直接调用sort方法，按自然顺序排序，即升序排序
        Collections.sort(lists);

        A aa = new A();
        aa.setName("aa");
        aa.setOrder(1);
        A bb = new A();
        bb.setName("bb");
        bb.setOrder(2);
        list.add(bb);
        list.add(aa);
        //list中的对象A实现Comparable接口
        Collections.sort(list);

        B ab = new B();
        ab.setName("ab");
        ab.setOrder("1");
        B ba = new B();
        ba.setName("ba");
        ba.setOrder("2");
        listB.add(ba);
        listB.add(ab);
        //根据Collections.sort重载方法来实现
        Collections.sort(listB,new Comparator<B>(){
            @Override
            public int compare(B b1, B b2) {
                return b1.getName().compareTo(b2.getName());
            }

        });

        System.out.println(lists);
        System.out.println(list);
        System.out.println(listB);

    }

}

class A implements Comparable<A>{
    private String name;
    private Integer id;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    @Override
    public String toString() {
        return "name is "+name+" id is "+id;
    }
    // 注意id要用Integer声明，不然下面return语句会出错！
    @Override
    public int compareTo(A a) {
        return this.id.compareTo(a.getId());
    }

}

class B{
    private String name;
    private String order;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getOrder() {
        return order;
    }
    public void setOrder(String order) {
        this.order = order;
    }
    @Override
    public String toString() {
        return "name is "+name+" order is "+order;
    }
}