用 Java 将列表转换为集合
原文:https://www.geeksforgeeks.org/convert-list-to-set-in-java/
Java Set 是 java.util 包的一部分，扩展了 java.util.Collection 接口。它不允许使用重复元素，最多只能容纳一个空元素。Java Set 接口的几个重要特性如下:
- set 接口是对象的无序集合，其中不能存储重复的值。
- Java 集合不提供对元素插入或删除位置的控制。
- 基本上，Set 是由 HashSet、LinkedHashSet 或 TreeSet(排序表示)实现的。
- Set 有各种添加、清除、大小等方法来增强这个界面的使用。
本文讨论了将一个列表界面转换为 Java 中的集合的不同方法:
-
Naive Approach: The naive solution is to create an empty set and add every element of the specified list to the newly created set.
下面是天真方法的实现:
```java // Java Program to convert // List to Set in Java 8
import java.util.; import java.util.stream.; import java.util.function.Function;
class GFG {
// Generic function to convert list to set public static Set convertListToSet(List list) { // create an empty set Set set = new HashSet<>();
// Add each element of list into the set for (T t : list) set.add(t);
// return the set return set; }
public static void main(String args[]) {
// Create a stream of integers List list = Arrays.asList("GeeksForGeeks", "Geeks", "forGeeks", "A computer portal", "for", "Geeks");
// Print the List System.out.println("List: " + list);
// Convert List to stream Set set = convertListToSet(list);
// Print the Set System.out.println("Set from List: " + set); } } ```
输出:
```java List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
```
-
Using Constructor: HashSet constructor can take another collection object to construct a new set containing the elements of the specied list.
下面是上述方法的实现:
```java // Java Program to convert // List to Set in Java 8
import java.util.; import java.util.stream.;
class GFG {
// Generic function to convert list to set public static Set convertListToSet(List list) { // create a set from the List return new HashSet<>(list); }
public static void main(String args[]) {
// Create a stream of integers List list = Arrays.asList("GeeksForGeeks", "Geeks", "forGeeks", "A computer portal", "for", "Geeks");
// Print the List System.out.println("List: " + list);
// Convert List to stream Set set = convertListToSet(list);
// Print the Set System.out.println("Set from List: " + set); } } ```
输出:
```java List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
```
-
Using Java 8 Stream API: HashSet constructor can take another collection object to construct a new set containing the elements of the specied list.
下面是上述方法的实现:
```java // Java Program to convert // List to Set in Java 8
import java.util.; import java.util.stream.;
class GFG {
// Generic function to convert list to set public static Set convertListToSet(List list) { // create a set from the List return list.stream().collect(Collectors.toSet()); }
public static void main(String args[]) {
// Create a stream of integers List list = Arrays.asList("GeeksForGeeks", "Geeks", "forGeeks", "A computer portal", "for", "Geeks");
// Print the List System.out.println("List: " + list);
// Convert List to stream Set set = convertListToSet(list);
// Print the Set System.out.println("Set from List: " + set); } } ```
输出:
```java List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
```
-
Using Guava Sets.newHashSet(): Sets.newHashSet() creates a mutable HashSet instance containing the elements of the specified list.
下面是上述方法的实现:
```java // Java Program to convert // List to Set in Java 8
import java.util.; import java.util.stream.;
class GFG {
// Generic function to convert list to set public static Set convertListToSet(List list) { // create a set from the List return return Sets.newHashSet(list); }
public static void main(String args[]) {
// Create a stream of integers List list = Arrays.asList("GeeksForGeeks", "Geeks", "forGeeks", "A computer portal", "for", "Geeks");
// Print the List System.out.println("List: " + list);
// Convert List to stream Set set = convertListToSet(list);
// Print the Set System.out.println("Set from List: " + set); } } ```
输出:
```java List: [GeeksForGeeks, Geeks, forGeeks, A computer portal, for, Geeks] Set from List: [Geeks, for, GeeksForGeeks, A computer portal, forGeeks]
```
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