Java8使List转为Map
代码语言：javascript
复制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));
}
}
