在java中附加arraylist

Question

Is it possible to concatenate two or more arraylist ? I have following case:

 private Arraylist<Double> getContextVectorsize(int sizeContext){
     ArrayList<Double> contextList = new ArrayList<Double>();
     for(int i =0 ; i< sizeContext; i++){
         contextList = //TODO 
     }   
}

I would like to append all the arraylist in order and want to generate an arraylist of size = sizeContext*ArraylistOfSingleMember

Answer 1

您可以使用 addAll() 方法。

Answer 2

Use list1.addAll(list2), this returns true if it worked AND updates list1. Here is a full code example from tutorialspoint.com.

import java.util.ArrayList;

public class ArrayListDemo {
   public static void main(String args[]) {

   // create an empty array list1 with an initial capacity
   ArrayList<Integer> arrlist = new ArrayList<Integer>(5);

   // use add() method to add elements in the list
   arrlist.add(12);
   arrlist.add(20);
   arrlist.add(45);

   // let us print all the elements available in list1
   System.out.println("Printing list1:");
   for (Integer number : arrlist) {
   System.out.println("Number = " + number);
   }

   // create an empty array list2 with an initial capacity
   ArrayList<Integer> arrlist2 = new ArrayList<Integer>(5);

   // use add() method to add elements in list2
   arrlist2.add(25);
   arrlist2.add(30);
   arrlist2.add(31);
   arrlist2.add(35);

   // let us print all the elements available in list2
   System.out.println("Printing list2:");
   for (Integer number : arrlist2) {
   System.out.println("Number = " + number);
   }

   // inserting all elements, list2 will get printed after list1
   arrlist.addAll(arrlist2);

   System.out.println("Printing all the elements");
   // let us print all the elements available in list1
   for (Integer number : arrlist) {
   System.out.println("Number = " + number);
   }
   }
}

Answer 3

for(int i =0 ; i< sizeContext; i++){
    contextList.addAll( an instance of ArrayList<Double>);
}