从 Java 的数组列表中移除所有元素
原文:https://www . geesforgeks . org/remove-all-elements-from-ArrayList-in-Java/
先决条件:Java 中的数组列表
给定一个数组列表，任务是移除 Java 中数组列表的所有元素。
示例:
Input: ArrayList = [1, 2, 3, 4]
Output: ArrayList = []
Input: ArrayList = [12, 23, 34, 45, 57, 67, 89]
Output: ArrayList = []
-
Using clear() method:
语法:
java collection_name.clear();清除()方法代码:
```java public void clear() { for (int i = 0; i < size; i++) list[i] = null;
size = 0;}
```
下面是上述方法的实现:
```java // Java Program for remove all elements ArrayList // Using clear() method
// import ArrayList package import java.util.ArrayList;
public class GFG {
// main method public static void main(String[] args) { // create empty ArrayList ArrayList list = new ArrayList<>();
// Adding elements of list list.add("Geeks"); list.add("for"); list.add("Geeks"); list.add("Gaurav");
// printing initial value ArrayList System.out.println("ArrayList: " + list);
// print size of ArrayList System.out.println("Size of ArrayList = " + list.size());
// remove all elements using clear() method list.clear();
// printing ArrayList System.out.println("\nAfter clear\n\n" + "ArrayList: " + list);
// print size of ArrayList after clear list System.out.println("Size of ArrayList = " + list.size()); } } ```
Output:
```java ArrayList: [Geeks, for, Geeks, Gaurav] Size of ArrayList = 4
After clear
ArrayList: [] Size of ArrayList = 0
```
时间复杂度:O(N)
-
Using removeAll() method
语法:
java collection_name.removeAll(collection_name);remove all()方法代码:
```java public boolean removeAll(Collection list) { boolean isModi = false; Iterator ite= iterator(); while (ite.hasNext()) { if (list.contains(ite.next())) { ite.remove(); isModi = true; } } return isModi; }
```
下面是上述方法的实现:
```java // Java Program for remove all elements ArrayList // Using removeAll() method
// import ArrayList package import java.util.ArrayList;
public class GFG {
// main method public static void main(String[] args) { // create empty ArrayList ArrayList list = new ArrayList<>();
// Adding elements of list list.add("Geeks"); list.add("for"); list.add("Geeks"); list.add("Gaurav");
// printing initial value ArrayList System.out.println("ArrayList: " + list);
// print size of ArrayList System.out.println("Size of ArrayList = " + list.size());
// remove all elements using clear() method list.removeAll(list);
// printing ArrayList System.out.println("\nAfter clear\n\n" + "ArrayList: " + list);
// print size of ArrayList after clear list System.out.println("Size of ArrayList = " + list.size()); } } ```
Output:
```java ArrayList: [Geeks, for, Geeks, Gaurav] Size of ArrayList = 4
After clear
ArrayList: [] Size of ArrayList = 0
```
时间复杂度:O(N^2)
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