首先创建两个实体类
@Data public class Student { //学号 private String no; //姓名 private String name; } @Data public class Teacher{ //教师号 private String no; //姓名 private String name; }
//声明一个List集合 Listlist = 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) ));
//声明一个List集合 Listlist = 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 ));
//声明一个List集合 Listlist = 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 ));
//声明一个List集合 Listlist = 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) );
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