Java Collections addAll()用法及代码示例

java.util.Collections类的addAll()方法用于将所有指定的元素添加到指定的集合中。要添加的元素可以单独指定或作为数组指定。此便捷方法的行为与c.addAll(Arrays.asList(elements))的行为相同，但是在大多数实现下，此方法的运行速度可能明显更快。

用法:

public static  boolean 
    addAll(Collection c, T... elements)

参数：此方法将以下参数作为参数

c-要插入元素的集合
elements-要插入c的元素

返回值：如果集合由于调用而发生更改，则此方法返回true。

异常：如果元素包含一个或多个null值并且c不允许为null元素，或者c或元素为null，则此方法引发NullPointerException

以下示例说明了addAll()方法

示例1:

// Java program to demonstrate 
// addAll() method 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) throws Exception 
    { 
        try { 
  
            // creating object of List<String> 
            List<String> arrlist = new ArrayList<String>(); 
  
            // Adding element to arrlist 
            arrlist.add("A"); 
            arrlist.add("B"); 
            arrlist.add("C"); 
            arrlist.add("Tajmahal"); 
  
            // printing the arrlist before operation 
            System.out.println("arrlist before operation : " + arrlist); 
  
            // add the specified element to specified Collections 
            // using addAll() method 
            boolean b = Collections.addAll(arrlist, "1", "2", "3"); 
  
            // printing the arrlist after operation 
            System.out.println("result : " + b); 
  
            // printing the arrlist after operation 
            System.out.println("arrlist after operation : " + arrlist); 
        } 
  
        catch (NullPointerException e) { 
  
            System.out.println("Exception thrown : " + e); 
        } 
        catch (IllegalArgumentException e) { 
  
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

输出：

arrlist before operation : [A, B, C, Tajmahal]
result : true
arrlist after operation : [A, B, C, Tajmahal, 1, 2, 3]

输出：

arrlist before operation : [A, B, C, Tajmahal]
result : true
arrlist after operation : [A, B, C, Tajmahal, 1, 2, 3]

示例2:对于NullPointerException

// Java program to demonstrate 
// addAll() method 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) throws Exception 
    { 
        try { 
  
            // creating object of List<String> 
            List<String> arrlist = new ArrayList<String>(); 
  
            // Adding element to arrlist 
            arrlist.add("A"); 
            arrlist.add("B"); 
            arrlist.add("C"); 
            arrlist.add("Tajmahal"); 
  
            // printing the arrlist before operation 
            System.out.println("arrlist before operation : " + arrlist); 
  
            // add the specified element to specified Collections 
            // using addAll() method 
            System.out.println("\nTrying to add the null value with arrlist"); 
            boolean b = Collections.addAll(null, arrlist); 
  
            // printing the arrlist after operation 
            System.out.println("result : " + b); 
  
            // printing the arrlist after operation 
            System.out.println("arrlist after operation : " + arrlist); 
        } 
  
        catch (NullPointerException e) { 
  
            System.out.println("Exception thrown : " + e); 
        } 
        catch (IllegalArgumentException e) { 
  
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

输出：

arrlist before operation : [A, B, C, Tajmahal]

Trying to add the null value with arrlist
Exception thrown : java.lang.NullPointerException

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 Collections addAll() 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。