java集合进行排序的方式总结

package test;

public class Emp implements Comparable {

    private String name;
    private int age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Emp() {
        super();
    }
    public Emp(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Emp [name=" + name + ", age=" + age + "]";
    }
    @Override
    public int compareTo(Object o) {
        if(o instanceof Emp){
            Emp emp = (Emp) o;
//          return this.age-emp.getAge();//按照年龄升序排序
            return this.name.compareTo(emp.getName());//换姓名升序排序
        }
        throw new ClassCastException("不能转换为Emp类型的对象...");
    }

}

package test;

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

import org.junit.BeforeClass;
import org.junit.Test;

public class TestSort {

    static List list = new ArrayList();
    //@BeforeClass注解标注的方法会在其它测试方法执行之前先执行,
    //且只执行一次.@Before注解标注的方法会在每个测试方法之前执行;
    //此处初始化集合只需要一次,因此使用@BeforeClass.
    @BeforeClass
    public static void init(){
        list.add(new Emp("tom",18));
        list.add(new Emp("jack",20));
        list.add(new Emp("rose",15));
        list.add(new Emp("jerry",17));
        System.out.println("排序前:");
        for(Object o : list){
            System.out.println(o);
        }
    }

    
//  @Test
//  public void testSortAge(){
//      Collections.sort(list);
//      System.out.println("自然排序按age排序后:");
//      for(Object o : list){
//          System.out.println(o);
//      }
//  }
//
    
    @Test
    public void testSortName(){
        Collections.sort(list);
        System.out.println("自然排序按name升序排序后:");
        for(Object o : list){
            System.out.println(o);
        }
    }

    
    @Test
    public void testComparatorSortAge(){
        Collections.sort(list,new Comparator () {
            @Override
            public int compare(Object o1, Object o2) {
                if(o1 instanceof Emp && o2 instanceof Emp){
                    Emp e1 = (Emp) o1;
                    Emp e2 = (Emp) o2;
                    return e1.getAge() - e2.getAge();
                }
                throw new ClassCastException("不能转换为Emp类型");
            }
        });
        System.out.println("使用Comparator比较器按age升序排序后:");
        for(Object o : list){
            System.out.println(o);
        }
    }
    
    @Test
    public void testComparatorSortName(){
        Collections.sort(list,new Comparator () {
            @Override
            public int compare(Object o1, Object o2) {
                if(o1 instanceof Emp && o2 instanceof Emp){
                    Emp e1 = (Emp) o1;
                    Emp e2 = (Emp) o2;
                    return e1.getName().compareTo(e2.getName());
                }
                throw new ClassCastException("不能转换为Emp类型");
            }
        });
        System.out.println("使用Comparator比较器按name升序排序后:");
        for(Object o : list){
            System.out.println(o);
        }
    }

}

测试代码：

自定义的比较器：
import java.util.Comparator;

public class MyComparator implements Comparator<Cell>{
	@Override
	public int compare(Cell o1, Cell o2) {
		return o1.getY()-o2.getY();//根据传入的cell的y坐标由小到大进行排序
	}
}
测试类：
 @Test
    public void testComparator() {
    	List<Cell> cells = new ArrayList<>();
    	cells.add(new Cell(2,3));
    	cells.add(new Cell(5,1));
    	cells.add(new Cell(3,2));
    	System.out.println(cells);//[Cell [x=2, y=3], Cell [x=5, y=1], Cell [x=3, y=2]]
    	MyComparator com = new MyComparator();
    	Collections.sort(cells,com);
    	System.out.println(cells);//根据自定义排序后的结果：[Cell [x=5, y=1], Cell [x=3, y=2], Cell [x=2, y=3]]
    } 

 @Test
    public void testComparator() {
    	List<Cell> cells = new ArrayList<>();
    	cells.add(new Cell(2,3));
    	cells.add(new Cell(5,1));
    	cells.add(new Cell(3,2));
    	System.out.println(cells);//[Cell [x=2, y=3], Cell [x=5, y=1], Cell [x=3, y=2]]
    	Collections.sort(cells,new Comparator<Cell>(){//此处创建了一个匿名内部类
		@Override
		public int compare(Cell o1,Cell o2){
			return o1.getY() - o2.getY();
		}

	});
    	System.out.println(cells);//[Cell [x=5, y=1], Cell [x=3, y=2], Cell [x=2, y=3]]
    }