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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