检查数组中的特定元素是否包含某个String。 然后删除该元素

Question

I have an ArrayList containing: [2x, 5, 6x]. I want to get rid of the elements containing the "x", but the contains() method applies to all of the elements in the ArrayList.

My attempt:

boolean ready = false;

while(!ready){
    if(first element in the array contains "x"){
    remove that element
    Check next element in line
}

When checked all the elements, and removed those which contains "x", set ready to true, and stop the loop. I want the output to just be: [6]. And then convert it to int, instead of String.

EDIT: I couldn't get it to work with ArrayList, because I couldn't alter the contents of an ArrayList. Therefore I changed it to a simple array. The array is now: String[]tokens = ligning2.split("-|\\+|\\*|\\/");

So the tokens array will keep [2x, 5, 6x]. So how do I delete the elements containing an x, with this kind of Array, instead of Arraylist?

Answer 1

This would be a great opportunity to utilize a lambda when calling List#removeIf .

For example:

List<String> list = Arrays.asList("2x", "5", "6x");

System.out.println(list); // [2x, 5, 6x]

list.removeIf(element -> element.contains("x"));

System.out.println(list); // [5]

Assuming that there can be multiple values that remain in the List which did not contain an "x", you can use a Stream to map each element to its integer value:

List<Integer> newList = list.stream()
                            .map(Integer::valueOf)
                            .collect(Collectors.toList());

The entire algorithm can be condensed into the following:

List<Integer> newList = list.stream()
                            .filter(element -> !element.contains("x"))
                            .map(Integer::valueOf)
                            .collect(Collectors.toList());

Answer 2

Easiest thing to do is using Stream s. These were added in Java 8 and you can use them in your case to filter certain items from the list and convert them to integers in one run:

List<String> elements = Arrays.asList("2x", "5", "6x");
List<Double> result = elements.stream()
     .filter(entry -> !entry.contains("x"))
     .map(Double::valueOf) //this assumes that all other entries are valid doubles
     .collect(Collectors.toList());

Answer 3

• Use an iterator to iterate the List
• for each iteration, if the current String contains the "x" String , remove it from the List with Iterator.remove();

For example :

   for (Iterator<String> iterator = list.iterator(); iterator.hasNext();) {
        String value = list.next();
        if(value.contains("x"){
           iterator.remove();
        }
    }

Answer 4

You can use an Iterator for example :

List<String> list = Arrays.asList("Hello", "xyz", "tkx");
Iterator<String> iter = list.iterator();
while (iter.hasNext()) {
    if(iter.next().contains("x")){//check if your element contain x
        iter.remove();//if yes remove it
    }
}

Answer 5

You can use this program

package com.anand;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.ListIterator;

public class ArrayListRemove {
static ArrayList<String> al=new ArrayList<>(Arrays.asList("6x","8","5x"));
public static void main(String[] args) {
    Iterator<String> i=al.iterator();
    while(i.hasNext())
    {
        if(i.next().toString().contains("x"))
        {
            i.remove();
        }
    }
    ListIterator<String> li= al.listIterator();
    while(li.hasNext())
    {
        System.out.println(li.next());
    }

}

}

Please let me know of you want to create a new Arraylist of integers or just the output to be integers. I will make changes accordingly