java排序和去重的几种常用方式
花了几天空闲功夫，亲自整理了一下，绝对实用！！
各位亲自跑一下，保证排序和去重就全懂了！（哪里不懂可以留言）
package com.hd.utility.vmda.utils;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;
import usedByUtils.EmployeeEntity;
import usedByUtils.EmployeeImplComparableEntity;
public class ComparatorUtils {
/**
* 排序（基本数据类型）：
*
* 方式一
*
* 默认方式
*/
public static void ComparatorSortBase1(List list) {
System.out.println("原：" + list.toString() + System.getProperty("line.separator"));
//1.直接排序，默认是正序
Collections.sort(list);
System.out.println("新：" + list.toString());
Collections.reverse(list);//反转
System.out.println("再反转：" + list.toString());
}
/**
* 排序（基本数据类型）：
*
* 方式二
*
* 顺序（正序或倒序）取决于“自定义实体类”中重写的compare()方法
*/
public static void ComparatorSortBase2(List list) {
System.out.println("原：" + list.toString() + System.getProperty("line.separator"));
//2.或者可以自定义顺序
Collections.sort(list, new Comparator() {
@Override
public int compare(Integer o1, Integer o2) {
int result = o2 - o1;// 倒序
//int result = o1 - o2;// 正序
return result;
}
});
System.out.println("新：" + list.toString());
}
/**
* 排序（根据“自定义实体类型”的某个属性）：
*
* 方式一
*
* 顺序（正序或倒序）取决于“自定义实体类”中重写的compare()方法
*/
public static void ComparatorSort1(List list) {
System.out.println("原：" + list.toString() + System.getProperty("line.separator"));
Collections.sort(list, new Comparator() {
@Override
public int compare(EmployeeEntity o1, EmployeeEntity o2) {
int result = o2.getEname().compareTo(o1.getEname());// 倒序
//int result = o1.getEname().compareTo(o2.getEname());// 正序
return result;
}
});
System.out.println("新：" + list.toString());
}
/**
* 排序（根据“自定义实体类型”的某个属性）：
*
* 方式二
*
* 实体类实现Comparable接口，并重写compare()方法
* 顺序（正序或逆序）取决于“自定义实体类”中重写的compare()方法
*/
public static void ComparatorSort2(List list) {
System.out.println("原：" + list.toString() + System.getProperty("line.separator"));
Collections.sort(list);
System.out.println("新：" + list.toString());
}
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
/**
* 去重（基本数据类型）：
*
* 方式一
*
* 根据set特性去重（3种set都可以）
*/
public static void ComparatorRemoveDuplicateBase(List list) {
System.out.println("原：" + list.toString() + System.getProperty("line.separator"));
//HashSet、TreeSet、LinkedHashSet都可以
HashSet set =new HashSet(list);
//或
//HashSet set =new HashSet();
//set.addAll(list);
//再赋值到“原”list
list.clear();
list.addAll(set);
//再赋值到“新”list
List listNew = new ArrayList(set);
System.out.println("去重（基本数据类型）set：\n" + set.toString());
System.out.println("去重（基本数据类型）list：\n" + list.toString());
System.out.println("去重（基本数据类型）listNew：\n" + listNew.toString());
}
/**
* 去重并排序（根据“自定义实体类型”的某个属性）：
*
* 方式一
*
* 根据set特性去重（3种set中，只有TreeSet提供了参数是Comparator的构造方法）
* 构造方法参数是Comparator，重写compare()方法
*/
public static void ComparatorRemoveDuplicate1(List list) {
System.out.println("原：" + list.toString() + System.getProperty("line.separator"));
//只有TreeSet可以//HashSet、LinkedHashSet都不行
Set set =new TreeSet<>(new Comparator() {
@Override
public int compare(EmployeeEntity o1, EmployeeEntity o2) {
//正序，将把所有员工按照自然顺序正序排列（这里是String，则按照ascii码升序排列，即字母顺序）
return o1.getEname().compareTo(o2.getEname());
//倒序
//return o2.getEname().compareTo(o1.getEname());
}
});
//list.clear();
//list.addAll(set);
set.addAll(list);
System.out.println("去重（自定义实体类型）set：\n" + set.toString());
}
/**
* 去重并排序（根据“自定义实体类型”的某个属性）：
*
* 方式二
*
* 实体类实现Comparable接口，并重写compare()方法
* 顺序（正序或逆序）取决于“自定义实体类”中重写的compare()方法
*/
public static void ComparatorRemoveDuplicate2(List list) {
System.out.println("原：" + list.toString() + System.getProperty("line.separator"));
Set set =new TreeSet<>();
//list.clear();
//list.addAll(set);
set.addAll(list);
System.out.println("去重（自定义实体类型）LinkedHashSet：\n" + set.toString());
}
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
public static void main(String[] args) {
List list = new ArrayList();
list.add(1);
list.add(3);
list.add(2);
list.add(4);
List empList = new ArrayList();
EmployeeEntity emp1 = new EmployeeEntity(2,"Guan YunChang");
EmployeeEntity emp2 = new EmployeeEntity(3,"Zhang Fei");
EmployeeEntity emp3 = new EmployeeEntity(1,"Liu Bei");
empList = Arrays.asList(emp1,emp2,emp3);
List empComparableList = new ArrayList();
EmployeeImplComparableEntity empC1 = new EmployeeImplComparableEntity(2,"Guan YunChang");
EmployeeImplComparableEntity empC2 = new EmployeeImplComparableEntity(3,"Zhang Fei");
EmployeeImplComparableEntity empC3 = new EmployeeImplComparableEntity(1,"Liu Bei");
empComparableList = Arrays.asList(empC1,empC2,empC3);
/**
* 看这里！！
*
* 释放下文对应的注释，即可查看对应的代码执行
*
* 看这里！！
*/
/*~~~~~~~~~~~~~~~~~排序~~~~~~~~~~~~~~~~~~*/
//一、一
//1.1.1排序（基本数据类型）//默认
//ComparatorUtils.ComparatorSortBase1(list);
//1.1.2排序（基本数据类型）
//ComparatorUtils.ComparatorSortBase2(list);
//一、二
//1.2.1排序（根据“自定义实体类型”的某个属性）
//ComparatorUtils.ComparatorSort1(empList);
//1.2.2排序（根据“自定义实体类型”的某个属性）//实体类通过实现Comparable接口并重写compare方法来实现！！
//ComparatorUtils.ComparatorSort2(empComparableList);
/*~~~~~~~~~~~~~~~~~排序~~~~~~~~~~~~~~~~~~*/
/*~~~~~~~~~~~~~~~~~去重~~~~~~~~~~~~~~~~~~*/
//二、一
//2.1.1去重（基本数据类型）
//list.add(2);
//ComparatorUtils.ComparatorRemoveDuplicateBase(list);
//二、二
//2.2.1去重并排序（根据“自定义实体类型”的某个属性）
//EmployeeEntity emp4 = new EmployeeEntity(4,"Liu Bei");
//List empListNew = new ArrayList(empList);//Arrays.asList生成的是不可变List
//empListNew.add(emp4);
//ComparatorUtils.ComparatorRemoveDuplicate1(empListNew);
//2.2.2去重并排序（根据“自定义实体类型”的某个属性）//实体类通过实现Comparable接口并重写compare方法来实现！！
//EmployeeImplComparableEntity empC4 = new EmployeeImplComparableEntity(4,"Liu Bei");
//List empListCNew = new ArrayList(empComparableList);//Arrays.asList生成的是不可变List
//empListCNew.add(empC4);
//ComparatorUtils.ComparatorRemoveDuplicate2(empListCNew);
/*~~~~~~~~~~~~~~~~~去重~~~~~~~~~~~~~~~~~~*/
}
}
附上，两个实体类：
EmployeeEntity.java
package usedByUtils;
public class EmployeeEntity {
private int empno;
private String ename;
public int getEmpno() {
return empno;
}
public void setEmpno(int empno) {
this.empno = empno;
}
public String getEname() {
return ename;
}
public void setEname(String ename) {
this.ename = ename;
}
public EmployeeEntity(int empno, String ename) {
super();
this.empno = empno;
this.ename = ename;
}
@Override
public String toString() {
return System.getProperty("line.separator") + "empno:" + empno + ";ename:" + ename + System.getProperty("line.separator");
}
}
EmployeeImplComparableEntity.java
package usedByUtils;
public class EmployeeImplComparableEntity implements Comparable{
private int empno;
private String ename;
public int getEmpno() {
return empno;
}
public void setEmpno(int empno) {
this.empno = empno;
}
public String getEname() {
return ename;
}
public void setEname(String ename) {
this.ename = ename;
}
public EmployeeImplComparableEntity(int empno, String ename) {
super();
this.empno = empno;
this.ename = ename;
}
@Override
public String toString() {
return System.getProperty("line.separator") + "empno:" + empno + ";ename:" + ename + System.getProperty("line.separator");
}
@Override
public int compareTo(EmployeeImplComparableEntity o) {
//员工姓名逆序
return o.getEname().compareTo(this.getEname());
}
}
花了几天空闲功夫，辛苦整理了一下，绝对实用！亲自跑一下保证排序和去重就全懂了。
觉得实用的点个赞哈！！鼓励我继续趟路，哈哈哈哈哈哈~~~~~~
灵感来自于以下两篇文章：
https://blog.csdn.net/qq_27409289/article/details/85316107
https://www.cnblogs.com/yw0219/p/7222108.html?utm_source=itdadao&utm_medium=referral