1+ package com .coding .basic ;
2+
3+ import java .util .Arrays ;
4+ import java .util .ConcurrentModificationException ;
5+ import java .util .NoSuchElementException ;
6+
7+ public class ArrayList implements List {
8+
9+ private Object [] elements ;
10+
11+ private int size ;
12+
13+ public ArrayList (int initialCapacity ) {
14+ super ();
15+ if (initialCapacity < 0 )
16+ throw new IllegalArgumentException ("Illegal Capacity: " + initialCapacity );
17+ this .elements = new Object [initialCapacity ];
18+ }
19+
20+ public ArrayList () {
21+ this (10 );
22+ }
23+
24+ public void add (Object obj ) {
25+ ensureCapacity (size + 1 );
26+ elements [size ++] = obj ;
27+
28+ }
29+
30+ public void add (int index , Object obj ) {
31+ rangeCheck (index );
32+ ensureCapacity (size + 1 );
33+ System .arraycopy (elements , index , elements , index + 1 , size - index );
34+ elements [index ] = obj ;
35+ size ++;
36+ }
37+
38+ public Object get (int index ) {
39+ rangeCheck (index );
40+ return elements [index ];
41+ }
42+
43+ public Object remove (int index ) {
44+ rangeCheck (index );
45+ Object toRemove = elements [index ];
46+ int numMoved = size - index - 1 ;
47+ if (numMoved > 0 )
48+ System .arraycopy (elements , index + 1 , elements , index , numMoved );
49+ elements [--size ] = null ;
50+ return toRemove ;
51+ }
52+
53+ public int size () {
54+ return size ;
55+ }
56+
57+ public Iterator iterator () {
58+ return new ArrayListIterator ();
59+ }
60+
61+ private void ensureCapacity (int minCapacity ) {
62+ int oldCapacity = elements .length ;
63+ if (minCapacity > oldCapacity ) {
64+ int newCapacity = oldCapacity * 2 ;
65+ if (newCapacity < minCapacity )
66+ newCapacity = minCapacity ;
67+ elements = Arrays .copyOf (elements , newCapacity );
68+ }
69+ }
70+
71+ private void rangeCheck (int index ) {
72+ if (index >= size )
73+ throw new IndexOutOfBoundsException (outOfBoundsMsg (index ));
74+ }
75+
76+ private String outOfBoundsMsg (int index ) {
77+ return "Index: " + index + ", Size: " + this .size ;
78+ }
79+
80+ private class ArrayListIterator implements Iterator {
81+
82+ private int pos = 0 ;
83+
84+ public boolean hasNext () {
85+ return pos != size ;
86+ }
87+
88+ public Object next () {
89+ int i = pos ;
90+ if (i >= size )
91+ throw new NoSuchElementException ();
92+ Object [] elements = ArrayList .this .elements ;
93+ if (i >= elements .length )
94+ throw new ConcurrentModificationException ();
95+ pos = i + 1 ;
96+ return (Object ) elements [i ];
97+ }
98+ }
99+
100+ }
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