集合自定义排序Comparable、Comparator

Comparable是在集合内部定义方法的排序，位于java.lang下。

Comparator是在集合外部实现的排序，位于java.util下。

 

Comparable 实现案例：

public class DeptBean implements Comparable<DeptBean>{

	private int deptId;
	private String departmentName;
	private int parentDepartmentId;
	private int orderIndex;
	
	public DeptBean() {
		super();
	}
	public DeptBean(int deptId, String departmentName, int orderIndex) {
		super();
		this.deptId = deptId;
		this.departmentName = departmentName;
		this.orderIndex = orderIndex;
	}

	@Override
	public String toString() {
		return "DeptBean [deptId=" + deptId + ", departmentName="
				+ departmentName + ", parentDepartmentId=" + parentDepartmentId
				+ ", orderIndex=" + orderIndex + ", childDept=" + childDept
				+ ", userList=" + userList + "]";
	}

	@Override
	public int compareTo(DeptBean o) {
		if(this.orderIndex < o.orderIndex){
			return -1;
		}else{
			return 1;
		}
	}
	public static void main(String[] args) {
		
		List<DeptBean> list = new ArrayList<DeptBean>();
		list.add(new DeptBean(1,"部门1",2));
		list.add(new DeptBean(2,"部门2",12));
		list.add(new DeptBean(3,"部门3",5));
		list.add(new DeptBean(4,"部门4",4));
		list.add(new DeptBean(5,"部门5",8));
		list.add(new DeptBean(6,"部门6",1));
		
		for(DeptBean dept : list){
			System.out.println(dept.getDepartmentName()+" "+dept.getOrderIndex());
		}
		
		Collections.sort(list);
		System.out.println("排序后");
		for(DeptBean dept : list){
			System.out.println(dept.getDepartmentName()+" "+dept.getOrderIndex());
		}
		
		
	}	

}

　　

Comparator 实现案例：

public class DeptBean{

	private int deptId;
	String departmentName;

	int orderIndex;

	public DeptBean() {
		super();
	}
	public DeptBean(int deptId, String departmentName, int orderIndex) {
		super();
		this.deptId = deptId;
		this.departmentName = departmentName;
		this.orderIndex = orderIndex;
	}
	

	
	public static void main(String[] args) {

		List<DeptBean> list = new ArrayList<DeptBean>();
		list.add(new DeptBean(1,"部门1",2));
		list.add(new DeptBean(2,"部门2",12));
		list.add(new DeptBean(3,"部门3",5));
		list.add(new DeptBean(4,"部门4",4));
		list.add(new DeptBean(5,"部门5",8));
		list.add(new DeptBean(6,"部门6",1));
		
		for(DeptBean dept : list){
			System.out.println(dept.departmentName+" "+dept.orderIndex);
		}
		MyComparator comparator = new MyComparator();
		Collections.sort(list,comparator);
		System.out.println("排序后");
		for(DeptBean dept : list){
			System.out.println(dept.departmentName+" "+dept.orderIndex);
		}
		
		
	}
}

public class MyComparator implements Comparator<DeptBean>{
	public int compare(DeptBean o1, DeptBean o2) {
		if(o1.orderIndex < o2.orderIndex){
			return -1;
		}else{
			return 1;
		}
	}
}

// 或者另一种写法
	public static void main(String[] args) {

		List<DeptBean> list = new ArrayList<DeptBean>();
		list.add(new DeptBean(1,"部门1",2));
		list.add(new DeptBean(2,"部门2",12));
		list.add(new DeptBean(3,"部门3",5));
		list.add(new DeptBean(4,"部门4",4));
		list.add(new DeptBean(5,"部门5",8));
		list.add(new DeptBean(6,"部门6",1));
		
		for(DeptBean dept : list){
			System.out.println(dept.departmentName+" "+dept.orderIndex);
		}
		
		Collections.sort(list,new Comparator<DeptBean>(){

			@Override
			public int compare(DeptBean o1, DeptBean o2) {
				if(o1.orderIndex > o2.orderIndex){  //如果o1.orderIndex > o2.orderIndex,返回正数，o1排在o2的后面，否则排在前面
					return 1;
				}else{
					return -1;
				}
			}
			
		});
		System.out.println("排序后");
		for(DeptBean dept : list){
			System.out.println(dept.departmentName+" "+dept.orderIndex);
		}
	}

　　如果map的集合需要根据值来排序，需要将map转成list，然后排序

 List<Map.Entry<Integer, DeptBean>> list = new ArrayList<Map.Entry<Integer, DeptBean>>(map1.entrySet());
	    Collections.sort(list, new Comparator<Map.Entry<Integer, DeptBean>>(){

			public int compare(Entry<Integer, DeptBean> o1,Entry<Integer, DeptBean> o2) {
				if(o1.getValue().getOrderIndex() < o2.getValue().getOrderIndex()){
					return 1;
				}else if(o1.getValue().getOrderIndex() < o2.getValue().getOrderIndex()){
					return -1;
				}else{
					return 0;
				}
			}
	    	
	    });
	    System.out.println("排序后");
	    for(Map.Entry<Integer, DeptBean> mapping : list){
	    	System.out.println(mapping.getKey()+" "+ mapping.getValue().getDepartmentName()+"  "+mapping.getValue().getOrderIndex());
	    }

　　

参考：https://blog.csdn.net/tolcf/article/details/52229068