list转map的三种方法( 二 ) _电脑

Student Student2 = new Student();
Student2.setId(2L);
Student2.setAge("13");

StudentList.add(Student1);
StudentList.add(Student2);

Map<Long, Student> maps = Maps.uniqueIndex(StudentList,
new Function<Student, Long>() {
@Override
public Long apply(Student student) {
return student.getId();
}
});

System.out.println(maps);

}
}

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2测试成果如下所示：

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第三种：利用JDK1.8 将list调集转map1将一个对象作为value放入map中
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

public class ListToMap {
public static void main(String[] args) {
List<Student> StudentList = new ArrayList<Student>();
Student Student1 = new Student();
Student1.setId(1L);
Student1.setAge("12");

Student Student2 = new Student();
Student2.setId(2L);
Student2.setAge("13");

Student Student3 = new Student();
Student3.setId(2L);
Student3.setAge("14");

StudentList.add(Student1);
StudentList.add(Student2);
StudentList.add(Student3);

/**
* List -> Map
* 需要注重的是：
* toMap 若是调集对象有反复的key ，会报错Duplicate key ....
* apple1,apple12的id都为1 。
* 可以用 (k1,k2)->k1 来设置，若是有反复的key,则保留key1,舍弃key2
* 或者可以用 (k1,k2)->k2 来设置，若是有反复的key,则保留key2,舍弃key1
*/
Map<Long, Student> maps = StudentList.stream().collect(Collectors.toMap(Student::getId,Function.identity(), (v1,v2)->v1));

System.out.println(maps);

}
}

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2将一个对象的属性作为value

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

public class ListToMap {
public static void main(String[] args) {
List<Student> StudentList = new ArrayList<Student>();
Student Student1 = new Student();
Student1.setId(1L);
Student1.setAge("12");