Java ArrayList ensureCapacity()用法及代码示例

如有必要，java.util.ArrayList类的ensureCapacity()方法会增加此ArrayList实例的容量，以确保它至少可以容纳最小容量参数指定的元素数量。

用法:

public void ensureCapacity(int minCapacity)

参数：该方法将所需的最小容量作为参数。

以下示例说明了ensureCapacity()方法。

示例1:

// Java program to demonstrate 
// ensureCapacity() method for Integer value 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) 
        throws Exception 
    { 
  
        try { 
  
            // Creating object of ArrayList<Integer> 
            ArrayList<Integer> 
                arrlist = new ArrayList<Integer>(); 
  
            // adding element to arrlist 
            arrlist.add(10); 
            arrlist.add(20); 
            arrlist.add(30); 
            arrlist.add(40); 
  
            // Print the ArrayList 
            System.out.println("ArrayList: "
                               + arrlist); 
  
            // ensure that the ArrayList 
            // can hold upto 5000 elements 
            // using ensureCapacity() method 
            arrlist.ensureCapacity(5000); 
  
            // Print 
            System.out.println("ArrayList can now"
                               + " surely store upto"
                               + " 5000 elements."); 
        } 
  
        catch (NullPointerException e) { 
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

输出：

ArrayList: [10, 20, 30, 40]
ArrayList can now surely store upto 5000 elements.

示例2:

// Java program to demonstrate 
// ensureCapacity() method for String value 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) 
        throws Exception 
    { 
  
        try { 
  
            // Creating object of ArrayList<Integer> 
            ArrayList<String> 
                arrlist = new ArrayList<String>(); 
  
            // adding element to arrlist 
            arrlist.add("A"); 
            arrlist.add("B"); 
            arrlist.add("C"); 
            arrlist.add("D"); 
  
            // Print the ArrayList 
            System.out.println("ArrayList: "
                               + arrlist); 
  
            // ensure that the ArrayList 
            // can hold upto 400 elements 
            // using ensureCapacity() method 
            arrlist.ensureCapacity(400); 
  
            // Print 
            System.out.println("ArrayList can now"
                               + " surely store upto"
                               + " 400 elements."); 
        } 
  
        catch (NullPointerException e) { 
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

输出：

ArrayList: [A, B, C, D]
ArrayList can now surely store upto 400 elements.

相关用法

注：本文由纯净天空筛选整理自RohitPrasad3大神的英文原创作品 ArrayList ensureCapacity() method in Java with Examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。