Java中的 Collections.nCopies()

Collections.nCopies()的作用是返回一个不可变列表，其中包含给定对象的 n 个副本。如果我们想创建一个包含 n 个给定对象副本的列表，这个函数会很有帮助。新分配的数据对象很小，即它包含对数据对象的单个引用。

句法 ：

public static  List nCopies(int number, T object)

where, number is the number of copies
of object and object represents the 
element which will appear number times
in the returned list. T represents generic type. 

异常：如果number的值小于 0，该函数将抛出IllegalArgumentException 。

例子 ：

Java

// Java code to show implementation
// of Collections.nCopies()
import java.util.*;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // creating a list where first argument
        // represents the number of copies and
        // the second argument represents the
        // element to be copied for 'number' times
        // This will create 4 copies of the objects.
        List list = Collections.nCopies(4, "GeeksforGeeks");
  
        // Displaying the list returned
        System.out.println("The list returned is :");
        Iterator itr = list.iterator();
        while (itr.hasNext()) {
            System.out.print(itr.next() + " ");
        }
        System.out.println("\n");
  
        List list1 = Collections.nCopies(3, "GeeksQuiz");
      
        // Displaying the list returned
        System.out.println("The list returned is :");
        Iterator itr1 = list1.iterator();  
        while (itr1.hasNext()) {
            System.out.print(itr1.next() + " ");
        }
        System.out.print("\n");
    }
}

输出 ：

The list returned is :
GeeksforGeeks GeeksforGeeks GeeksforGeeks GeeksforGeeks 

The list returned is :
GeeksQuiz GeeksQuiz GeeksQuiz