首先创建两个实体类 @Datapublic class Student { //学号 private String no; //姓名 private String name;}@Datapublic class
首先创建两个实体类
@Datapublic class Student { //学号 private String no; //姓名 private String name;}@Datapublic class Teacher{ //教师号 private String no; //姓名 private String name; }
List
转 Map
//声明一个List集合List list = new ArrayList(); list.add(new Student("1001", "小A")); list.add(new Student("1001", "小B"));//学号重复(下面特殊处理) list.add(new Student("1002", "小C")); list.add(new Student("1003", "小D")); //将list转map 【key为1个属性,value为1个属性】 Map map =list.stream().collect(Collectors.toMap( Student::getNo, Student::getName, (key1 , key2) -> key1 //(map的键重复不会报错,下面已经处理)));//将list转map 【key为多个属性,value为1个属性】 Map map =list.stream().collect(Collectors.toMap( obj -> obj.getNo() + "_" + obj.getName(),Student::getName, (key1 , key2) -> key1 //(map的键重复不会报错,下面已经处理)));
List
转 Map
(返回对象本身)//声明一个List集合List list = new ArrayList();list.add(new Student("1001", "小A"));list.add(new Student("1001", "小B"));list.add(new Student("1002", "小C"));list.add(new Student("1003", "小D"));//将list转map 【key为1个属性,value为对象本身】 (map的键去重)Map map = list.stream().collect(Collectors.toMap( Student::getNo, obj -> obj, (key1 , key2) -> key1 )); 或者//将list转map 【key为1个属性,value为对象本身】 (map的键去重)Map map = list.stream().collect(Collectors.toMap( Student::getNo, Function.identity(), (key1 , key2) -> key1 )); 或者//将list转map 【key为多个属性,value为对象本身】 (map的键去重)Map map = list.stream().collect(Collectors.toMap( obj -> obj.getNo() + "_" + obj.getName(), obj -> obj, (key1 , key2) -> key1 ));
List
转 Map
(返回另一个对象)//声明一个List集合List list = new ArrayList();list.add(new Student("1001", "小A"));list.add(new Student("1001", "小B"));list.add(new Student("1002", "小C"));list.add(new Student("1003", "小D"));//将list转map 【key为1个属性,value为另一个对象】 (map的键去重)Map map = list.stream().collect(Collectors.toMap( Student::getNo, stu -> { Teacher teacher = new Teacher(); teacher.setNo(stu.getNo()); teacher.setName(stu.getName()); return teacher; }, (key1 , key2) -> key1));
List
转 Map>
(分组)【以1个字段分/以多个字段分】//声明一个List集合List list = new ArrayList(); list.add(new Student("1001", "小A")); list.add(new Student("1001", "小B")); list.add(new Student("1002", "小C")); list.add(new Student("1003", "小D"));//将list转map 【key为1个属性,value为相同key的集合】 (以某1个属性来分组,将分组后相同的对象放在一起)Map> map = list.stream().collect( Collectors.groupingBy(Student::getNo) );//将list转map 【key为多个属性,value为相同key的集合】 (以多个属性来分组,将分组后相同的对象放在一起)Map> map = list.stream().collect( Collectors.groupingBy(obj -> obj.getNo + "_" + obj.getName) );
来源地址:https://blog.csdn.net/SHYLOGO/article/details/129381152
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本文标题: Java 8中List转Map的多种方式
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