list的去重，需要重写equals与hashCode

柔光的暖阳◎ 2022-03-29 13:49 303阅读 0赞

去重方法一：  
set去重

package com.hzbank.counter.bean;
    
    import com.fasterxml.jackson.annotation.JsonFormat;
    
    public class ReportFormsDialogue {
    
        private String name;
    
        private String usernameId;
    
        public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	public String getUsernameId() {
    		return usernameId;
    	}
    	public void setUsernameId(String usernameId) {
    		this.usernameId = usernameId;
    	}
    
        @Override
        public boolean equals(Object obj) {
            ReportFormsDialogue s=(ReportFormsDialogue)obj;
            return usernameId.equals(s.usernameId) && name.equals(s.name);
        }
        @Override
        public int hashCode() {
            String in = usernameId + name;
            return in.hashCode();
        }
    }

public class Test {
      
     public static void main(String[] args) {
     List<ReportFormsDialogue> stu = new ArrayList<ReportFormsDialogue>();
     stu.add(new ReportFormsDialogue("1","yi"));
     stu.add(new ReportFormsDialogue("3","san"));
     stu.add(new ReportFormsDialogue("3","san"));
     stu.add(new ReportFormsDialogue("2","er"));
     stu.add(new ReportFormsDialogue("2","er"));
     //set集合保存的是引用不同地址的对象
     Set<ReportFormsDialogue> ts = new HashSet<ReportFormsDialogue>();
     ts.addAll(stu);
      
     for (ReportFormsDialogue reportFormsDialogue: ts) {
      System.out.println(reportFormsDialogue. getName()+"-"+reportFormsDialogue.getUsernameId());
     }
     }
    }

第二种方法：  
使用distinct关键词

@Select(value = {
                "<script>" +
                "SELECT distinct username_id,nameFROM total_chatre_cords" +
                "<where>" +
                "<if test=\"name != null and name !=''\">\n" +
                "AND name=#{name} \n" +
                "</if>\n" +
                  "<if test=\"usernameId != null and usernameId !=''\">\n" +
                "AND username_id=#{usernameId} \n" +
                "</if>" +
                "</where>" +
                "</script>"
        })
        List<TotalChatreCords> getTotalChartByAll(@Param("name")String name,@Param("usernameId")String usernameId);