Java三种方法将List转换为Map的实例

1.for循环

import com.google.common.base.function;
import com.google.common.collect.maps;
import java.util.arraylist;
import java.util.hashmap;
import java.util.list;
import java.util.map;
public class listtomap {
  public static void main(string[] args) {
    list<user> userlist = new arraylist<>();
    user user1 = new user();
    user1.setid(1l);
    user1.setage("12");
    user user2 = new user();
    user2.setid(2l);
    user2.setage("13");
    userlist.add(user1);
    userlist.add(user2);
    map<long, user> maps = new hashmap<>();
    for (user user : userlist) {
      maps.put(user.getid(), user);
    }
    system.out.println(maps);
  }
  public static class user {
    private long id;
    private string age;
    public long getid() {
      return id;
    }
    public void setid(long id) {
      this.id = id;
    }
    public string getage() {
      return age;
    }
    public void setage(string age) {
      this.age = age;
    }
    @override
    public string tostring() {
      return "user{" +
          "id=" + id +
          ", age='" + age + '\'' +
          '}';
    }
  }
}

2.使用guava

map<long, user> maps = maps.uniqueindex(userlist, new function<user, long>() {
      @override
      public long apply(user user) {
        return user.getid();
      }
});

3.使用jdk1.8

map<long, user> maps = userlist.stream().collect(collectors.tomap(user::getid, user -> user));

看来还是使用jdk 1.8方便一些。

总结

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