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A basic ArrayList implementation(Java)
package me.wwsun.list;
import java.util.Iterator;
/**
*
* @param <E> is the type of elements in this list
*/
public class MyArrayList<E> implements Iterable<E> {
private static final int DEFAULT_CAPACITY = 10;
private int theSize;
private E[] theItems;
public MyArrayList() {
clear();
}
public void clear() {
theSize = 0;
ensureCapacity(DEFAULT_CAPACITY);
}
public void ensureCapacity(int newCapacity) {
if (newCapacity < theSize) return;
E[] old = theItems;
theItems = (E[]) new Object[newCapacity];
for (int i = 0; i < size(); i++) {
theItems[i] = old[i];
}
}
public int size() {
return theSize;
}
public boolean isEmpty() {
return size() == 0;
}
public void trimToSize() {
ensureCapacity(size());
}
public E get(int index) {
if (index < 0 || index >= size()) throw new ArrayIndexOutOfBoundsException();
return theItems[index];
}
public E set(int index, E newVal) {
if (index < 0 || index >= size()) throw new ArrayIndexOutOfBoundsException();
E old = theItems[index];
theItems[index] = newVal;
return old;
}
/**
* add the element to the end of list
*
* @param element is the element you want to add
* @return true if add successfully, otherwise return false
*/
public boolean add(E element) {
add(size(), element);
return true;
}
/**
* add the element to the specific position
*
* @param index is the position you want to insert the element
* @param element is the element you want to insert
*/
public void add(int index, E element) {
if (theItems.length == size()) ensureCapacity(size() * 2 + 1);
for (int i = theSize; i > index; i--) {
theItems[i] = theItems[i - 1];
}
theItems[index] = element;
theSize++;
}
public E remove(int index) {
E removeItem = theItems[index];
for (int i = index; i < size() - 1; i++) {
theItems[i] = theItems[i + 1];
}
theSize--;
return removeItem;
}
public Iterator<E> iterator() {
return new ArrayListIterator();
}
// inner class
private class ArrayListIterator implements java.util.Iterator<E> {
private int current = 0;
public boolean hasNext() {
return current < size();
}
public E next() {
if (!hasNext()) throw new java.util.NoSuchElementException();
return theItems[current++];
}
public void remove() {
MyArrayList.this.remove(--current); // reference the outer class
}
}
}
@AxelStein
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AxelStein commented Jan 10, 2021

DEFAULT_CAPACITY should be a power of two

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