Remove a specific string from an array of string

问题:

I have an array like this:

String n[] = {"google","microsoft","apple"};

What I want to do is to remove "apple".

My problem is very basic,however,I searched the website and I found out that java doesn't really support the deleting feature from an array.I also heard to use Java Utils, because it's so simple to remove an item....I tried to find Java Utils on google, but almost all links are dead.

So finally...is there any way to remove a string from an array of string?

Even if I use an ArrayList I can't find a method to generate a random item in it! For ex: in a normal array I generate a string like this:

String r = myAL[rgenerator.nextInt(myAL.length)];

In an arraylist it doesn't work....maybe you know a solution...

回答1:

Define "remove".

Arrays are fixed length and can not be resized once created. You can set an element to null to remove an object reference;

for (int i = 0; i < myStringArray.length(); i++)
{
    if (myStringArray[i].equals(stringToRemove))
    {
        myStringArray[i] = null;
        break;
    }
}

or

myStringArray[indexOfStringToRemove] = null;

If you want a dynamically sized array where the object is actually removed and the list (array) size is adjusted accordingly, use an ArrayList<String>

myArrayList.remove(stringToRemove); 

or

myArrayList.remove(indexOfStringToRemove);

Edit in response to OP's edit to his question and comment below

String r = myArrayList.get(rgenerator.nextInt(myArrayList.size()));

回答2:

It is not possible in on step or you need to keep the reference to the array. If you can change the reference this can help:

      String[] n = new String[]{"google","microsoft","apple"};
      final List<String> list =  new ArrayList<String>();
      Collections.addAll(list, n); 
      list.remove("apple");
      n = list.toArray(new String[list.size()]);

I not recommend the following but if you worry about performance:

      String[] n = new String[]{"google","microsoft","apple"};
      final String[] n2 = new String[2]; 
      System.arraycopy(n, 0, n2, 0, n2.length);
      for (int i = 0, j = 0; i < n.length; i++)
      {
        if (!n[i].equals("apple"))
        {
          n2[j] = n[i];
          j++;
        }      
      }

I not recommend it because the code is a lot more difficult to read and maintain.

回答3:

Arrays in Java aren't dynamic, like collection classes. If you want a true collection that supports dynamic addition and deletion, use ArrayList<>. If you still want to live with vanilla arrays, find the index of string, construct a new array with size one less than the original, and use System.arraycopy() to copy the elements before and after. Or write a copy loop with skip by hand, on small arrays the difference will be negligible.

回答4:

You can't remove anything from an array - they're always fixed length. Once you've created an array of length 3, that array will always have length 3.

You'd be better off with a List<String>, e.g. an ArrayList<String>:

List<String> list = new ArrayList<String>();
list.add("google");
list.add("microsoft");
list.add("apple");
System.out.println(list.size()); // 3

list.remove("apple");
System.out.println(list.size()); // 2

Collections like this are generally much more flexible than working with arrays directly.

EDIT: For removal:

void removeRandomElement(List<?> list, Random random)
{
    int index = random.nextInt(list.size());
    list.remove(index);
}

回答5:

import java.util.*;

class Array {
    public static void main(String args[]) {
        ArrayList al = new ArrayList();
        al.add("google");
        al.add("microsoft");
        al.add("apple");
        System.out.println(al);
        //i only remove the apple//
        al.remove(2);
        System.out.println(al);
    }
}