J260713/授课代码/c260804/src/course/ToMapDemo.java

package course;

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

/**
 * @author WanJl
 * @version 1.0
 * @title ToMapDemo
 * @description
 * @create 2026/8/4
 */
public class ToMapDemo {
    public static void main(String[] args) {
        Student s1 = new Student(1001, "项羽");
        Student s2 = new Student(1002, "张良");
        Student s3 = new Student(1003, "项庄");
        Student s4 = new Student(1004, "刘邦");
        Student s5 = new Student(1005, "萧何");
        Student s6 = new Student(1006, "韩信");
        Student s7 = new Student(1007, "樊哙");
        ArrayList<Student> list = new ArrayList<>(List.of(s1, s2, s3, s4, s5, s6, s7));

        /*
        public static <T, K, U> Collector<T, ?, Map<K,U>>
        toMap
        (
        Function<? super T, ? extends K> keyMapper,
        Function<? super T, ? extends U> valueMapper
        )


            贪心思想----局部最优解，不代表全局最优解

         */



        Map<Integer,Student>map=list    //集合对象
            .stream()
                .collect(Collectors.toMap(
                        student->student.getId()//键
                        ,
                        student->student    //值
                ));
        System.out.println(map);

        Map<Integer,Student>map1=list    //集合对象
                .stream()
                .collect(Collectors.toMap(
                        new Function<Student, Integer>() {
                            @Override
                            public Integer apply(Student student) {
                                return student.getId();
                            }
                        }
                        ,
                        new Function<Student, Student>() {
                            @Override
                            public Student apply(Student student) {
                                return student;
                            }
                        }
                ));




    }
}