java howto ArrayList push, pop, shift, and unshift

Question

I've determined that a Java ArrayList.add is similar to a JavaScript Array.push

I'm stuck on finding ArrayList functions similar to the following

• Array.pop
• Array.shift
• Array.unshift I'm leaning toward ArrayList.remove[At]

Answer 1

ArrayList is unique in its naming standards. Here are the equivalencies:

Array.push    -> ArrayList.add(Object o); // Append the list
Array.pop     -> ArrayList.remove(int index); // Remove list[index]
Array.shift   -> ArrayList.remove(0); // Remove first element
Array.unshift -> ArrayList.add(int index, Object o); // Prepend the list

Note that unshift does not remove an element, but instead adds one to the list. Also note that corner-case behaviors are likely to be different between Java and JS, since they each have their own standards.

Answer 2

I was facing with this problem some time ago and I found java.util.LinkedList is best for my case. It has several methods, with different namings, but they're doing what is needed:

push()    -> LinkedList.addLast(); // Or just LinkedList.add();
pop()     -> LinkedList.pollLast();
shift()   -> LinkedList.pollFirst();
unshift() -> LinkedList.addFirst();

Answer 3

maybe you want to take a look java.util.Stack class. it has push, pop methods. and implemented List interface.

for shift/unshift, you can reference @Jon's answer.

however, something of ArrayList you may want to care about , arrayList is not synchronized. but Stack is. (sub-class of Vector). If you have thread-safe requirement, Stack may be better than ArrayList.

Answer 4

Great Answer by Jon.

I'm lazy though and I hate typing, so I created a simple cut and paste example for all the other people who are like me. Enjoy!

import java.util.ArrayList;
import java.util.List;

public class Main {

    public static void main(String[] args) {

        List<String> animals = new ArrayList<>();

        animals.add("Lion");
        animals.add("Tiger");
        animals.add("Cat");
        animals.add("Dog");

        System.out.println(animals); // [Lion, Tiger, Cat, Dog]

        // add() -> push(): Add items to the end of an array
        animals.add("Elephant");
        System.out.println(animals);  // [Lion, Tiger, Cat, Dog, Elephant]

        // remove() -> pop(): Remove an item from the end of an array
        animals.remove(animals.size() - 1);
        System.out.println(animals); // [Lion, Tiger, Cat, Dog]

        // add(0,"xyz") -> unshift(): Add items to the beginning of an array
        animals.add(0, "Penguin");
        System.out.println(animals); // [Penguin, Lion, Tiger, Cat, Dog]

        // remove(0) -> shift(): Remove an item from the beginning of an array
        animals.remove(0);
        System.out.println(animals); // [Lion, Tiger, Cat, Dog]

    }

}

Answer 5

Underscore-java library contains methods push(values), pop(), shift() and unshift(values).

Code example:

import com.github.underscore.Underscore:

List<String> strings = Arrays.asList("one", "two", " three");
List<String> newStrings = Underscore.push(strings, "four", "five");
// ["one", " two", "three", " four", "five"]
String newPopString = Underscore.pop(strings).fst();
// " three"
String newShiftString = Underscore.shift(strings).fst();
// "one"
List<String> newUnshiftStrings = Underscore.unshift(strings, "four", "five");
// ["four", " five", "one", " two", "three"]