Java8使List转为Map
- java8新特性
- 时间：2020-05-29 23:58
- 4403人已阅读
简介
在开发中，我们会经常遇到list转map的情况，那么本文就来介绍在JDK1.8下使用lambad表达式来实现list转map
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Java8使List转为Map
import com.kaigejava;
import javax.jws.soap.SOAPBinding;
import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;
public class Main {
public static void main(String[] args) {
List<User> userlist = new ArrayList<>();
for (int i = 0; i <10; i++) {
userlist.add(new User("张三"+i,i));
}
System.out.println(getAllages(userlist).size());
System.out.println(getUser2Map(userlist));
System.out.println(getUser2MapUser(userlist));
System.out.println(getUser2MapUser2(userlist));
System.out.println(getUser2MapUser3(userlist));
}
public static List<Integer> getAllages(List<User>userlist){
return userlist.stream().map(user -> user.getAge()).collect(Collectors.toList());
}
public static Map<Integer,String> getUser2Map(List<User>userlist){
return userlist.stream().collect(Collectors.toMap(User::getAge,User::getName));
}
public static Map<Integer,User> getUser2MapUser(List<User>userlist){
return userlist.stream().collect(Collectors.toMap(User::getAge,User-> User));
}
/**
* 比较优雅的写法是这样的
* @param userlist
* @return
*/
public static Map<Integer,User> getUser2MapUser2(List<User>userlist){
return userlist.stream().collect(Collectors.toMap(User::getAge, Function.identity()));
}
/**
* 重复key的情况下 简单的使用后者覆盖前者的
*/
public static Map<Integer,User> getUser2MapUser3(List<User>userlist){
return userlist.stream().collect(Collectors.toMap(User::getAge, Function.identity(),(key1,key2)->key2));
}
/**
*指定map的具体实现
* @param userlist
* @return
*/
public static Map<Integer,User> getUser2MapUser4(List<User>userlist){
return userlist.stream().collect(Collectors.toMap(User::getAge, Function.identity(),(key1,key2)->key2, LinkedHashMap::new));
}
}