Contents of page :
1) Methods used in custom ArrayList in java-
public void add(E value)
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Add objects in ArrayListCustom
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public E get(int index)
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Method returns element on specific index.
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public Object remove(int index)
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Method returns removedElement on specific index, else it throws IndexOutOfBoundException if index is negative or greater than size of size.
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public void display()
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-Method displays all objects in ArrayListCustom.
-Insertion order is guaranteed.
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private void ensureCapacity()
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Method increases capacity of list by making it double.
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package com.ankit;
import java.util.Arrays;
class Employee {
private String id;
private String name;
/**
* Employee constructor
*/
public Employee(String id, String name) { // constructor
this.id = id;
this.name = name;
}
@Override
public String toString() {
return "Employee[id=" + id + ", name=" + name + "] ";
}
}
/** Copyright (c), AnkitMittal JavaMadeSoEasy.com */
/**
* @author AnkitMittal
* Copyright (c), AnkitMittal . All Contents are copyrighted and must not be reproduced in any form.
* This class provides custom implementation of ArrayList(without using java api's)
* Insertion order of objects is maintained.
* Implementation allows you to store null as well.
* @param <E>
*/
class ArrayListCustom<E> {
private static final int INITIAL_CAPACITY = 10;
private Object elementData[]={};
private int size = 0;
/**
* constructor.
*/
public ArrayListCustom() {
elementData = new Object[INITIAL_CAPACITY];
}
/**
* method adds elements in ArrayListCustom.
*/
public void add(E e) {
if (size == elementData.length) {
ensureCapacity(); //increase current capacity of list, make it double.
}
elementData[size++] = e;
}
/**
* method returns element on specific index.
*/
@SuppressWarnings("unchecked")
public E get(int index) {
if ( index <0 || index>= size) { //if index is negative or greater than size of size, we throw Exception.
throw new IndexOutOfBoundsException("Index: " + index + ", Size " + index);
}
return (E) elementData[index]; //return value on index.
}
/**
* method returns removedElement on specific index.
* else it throws IndexOutOfBoundException if index is negative or greater than size of size.
*/
public Object remove(int index) {
if ( index <0 || index>= size) { //if index is negative or greater than size of size, we throw Exception.
throw new IndexOutOfBoundsException("Index: " + index + ", Size " + index);
}
Object removedElement=elementData[index];
for(int i=index;i<size - 1;i++){
elementData[i]=elementData[i+1];
}
size--; //reduce size of ArrayListCustom after removal of element.
return removedElement;
}
/**
* method increases capacity of list by making it double.
*/
private void ensureCapacity() {
int newIncreasedCapacity = elementData.length * 2;
elementData = Arrays.copyOf(elementData, newIncreasedCapacity);
}
/**
* method displays all the elements in list.
*/
public void display() {
System.out.print("Displaying list : ");
for(int i=0;i<size;i++){
System.out.print(elementData[i]+" ");
}
}
}
/** Copyright (c), AnkitMittal JavaMadeSoEasy.com */
/**
* Main class to test ArrayListCustom functionality.
*/
public class ArrayListEmployee {
public static void main(String...a) {
ArrayListCustom<Employee> list = new ArrayListCustom<Employee>();
list.add(new Employee("1", "sam"));
list.add(new Employee("2", "amy"));
list.add(new Employee("3", "wil"));
list.add(new Employee("4", "cat"));
list.add(new Employee("1", "sam"));
list.add(new Employee("2", "amy"));
list.add(null);
list.display();
System.out.println("\nelement at index "+1+" = "+list.get(1));
System.out.println("element removed from index "+1+" = "+list.remove(1));
System.out.println("\nlet's display list again after removal at index 1");
list.display();
//list.remove(11); //will throw IndexOutOfBoundsException, because there is no element to remove on index 11.
//list.get(11); //will throw IndexOutOfBoundsException, because there is no element to get on index 11.
}
}
/*Output
Displaying list : Employee[id=1, name=sam] Employee[id=2, name=amy] Employee[id=3, name=wil] Employee[id=4, name=cat] Employee[id=1, name=sam] Employee[id=2, name=amy] null
element at index 1 = Employee[id=2, name=amy]
element removed from index 1 = Employee[id=2, name=amy]
let's display list again after removal at index 1
Displaying list : Employee[id=1, name=sam] Employee[id=3, name=wil] Employee[id=4, name=cat] Employee[id=1, name=sam] Employee[id=2, name=amy] null
*/
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