Java 删除ArrayList中的所有元素

前提是。Java中的ArrayList

给定一个ArrayList，任务是在Java中删除ArrayList的所有元素。

例子
输入: ArrayList = [1, 2, 3, 4]
输出: ArrayList = []

输入: ArrayList = [12, 23, 34, 45, 57, 67, 89]
输出: ArrayList = []

• 使用 clear() 方法:

语法:

collection_name.clear();

** clear()方法的代码：**

public void clear() {
    for (int i = 0; i < size; i++)
        list[i] = null;

    size = 0;
}

以下是上述步骤的实现。

// 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<String> 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());
    }
}

输出:

ArrayList: [Geeks, for, Geeks, Gaurav]
Size of ArrayList = 4

After clear

ArrayList: []
Size of ArrayList = 0

时间复杂度O(N)

使用removeAll()方法

语法:

collection_name.removeAll(collection_name);

** removeAll()方法的代码：**

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;
}

以下是上述步骤的实现。

// 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<String> 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());
    }
}

输出:

ArrayList: [Geeks, for, Geeks, Gaurav]
Size of ArrayList = 4

After clear

ArrayList: []
Size of ArrayList = 0

时间复杂度O(N^2)