stream.collect(Collectors.toList())去重问题

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我是靠谱客的博主单薄咖啡，这篇文章主要介绍stream.collect(Collectors.toList())去重问题，现在分享给大家，希望可以做个参考。

java8 stream源码中stream.collect(Collectors.toList())去重

**
利用 java8 stream对list或者set中带有(“aaa”,“88888”)等复杂字段去重。如若失败可能是equals方法原因，需要重写hashCode()， equals(Object obj)方法。
测试发现如果hashCode()的字段为Long类型，即不是String的话equals(Object obj)方法中的this.id==other.getId()应将换成this.id.equals(other.getId()，测试即可成功。
需要的朋友可可参考一下如下代码。
菜鸟小白zzh分享

复制代码

package zzh;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
public class Test {
    public static void main(String[] args) {
        EqualsObj obj1 =new EqualsObj("1","xxx");
        EqualsObj obj2 =new EqualsObj("1","88888");
        EqualsObj obj3 =new EqualsObj("2","xxx");
        List<EqualsObj> list = new ArrayList<>();
        list.add(obj1);
        list.add(obj2);
        list.add(obj3);
        list =  list.stream().distinct().collect(Collectors.toList());
        Set<EqualsObj> set = new HashSet<>();
        set.add(obj1);
        set.add(obj2);
        set.add(obj3);
    }
    static class EqualsObj{
        private String id;
        private String name;
        public EqualsObj(String id,String name){
            this.id = id;
            this.name = name;
        }
        public String getId() {
            return id;
        }
        public void setId(String id) {
            this.id = id;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        @Override
        public int hashCode() {
            int result = 17;
            result = 31 * result + (id == null ? 0 : id.hashCode());
            return result;
        }
        @Override
        public boolean equals(Object obj) {
            //地址相等
            if(this == obj){
                return true;
            }
            if(obj == null){
                //非空性：对于任意非空引用x，x.equals(null)应该返回false。
                return false;
            }
            if(obj instanceof EqualsObj){
                EqualsObj other = (EqualsObj) obj;
                //需要比较的字段相等，则这两个对象相等
                if(this.id==other.getId()){
                    return true;
                }
            }
            return false;
        }
    }
}

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package zzh;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
public class Test {
    public static void main(String[] args) {
        EqualsObj obj1 =new EqualsObj("1","xxx");
        EqualsObj obj2 =new EqualsObj("1","88888");
        EqualsObj obj3 =new EqualsObj("2","xxx");
        List<EqualsObj> list = new ArrayList<>();
        list.add(obj1);
        list.add(obj2);
        list.add(obj3);
        list =  list.stream().distinct().collect(Collectors.toList());
        Set<EqualsObj> set = new HashSet<>();
        set.add(obj1);
        set.add(obj2);
        set.add(obj3);
    }
    static class EqualsObj{
        private String id;
        private String name;
        public EqualsObj(String id,String name){
            this.id = id;
            this.name = name;
        }
        public String getId() {
            return id;
        }
        public void setId(String id) {
            this.id = id;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        @Override
        public int hashCode() {
            int result = 17;
            result = 31 * result + (id == null ? 0 : id.hashCode());
            return result;
        }
        @Override
        public boolean equals(Object obj) {
            //地址相等
            if(this == obj){
                return true;
            }
            if(obj == null){
                //非空性：对于任意非空引用x，x.equals(null)应该返回false。
                return false;
            }
            if(obj instanceof EqualsObj){
                EqualsObj other = (EqualsObj) obj;
                //需要比较的字段相等，则这两个对象相等
                if(this.id==other.getId()){
                    return true;
                }
            }
            return false;
        }
    }
}