public
class My
ArrayList {
private
Object[] elementData;
private
int
size;
public
int
size() {
return
size;
}
public
boolean
isEmpty() {
return
size ==
0
;
}
public My
ArrayList() {
this
(
10
);
}
public My
ArrayList(
int
initialCapacity) {
if
(initialCapacity <
0
) {
try
{
throw
new
Exception();
}
catch
(Exception e) {
e.printStackTrace();
}
}
elementData =
new
Object[initialCapacity];
}
public
void
add(Object obj) {
// 数组扩容
if
(size == elementData.length) {
Object[] newArray =
new
Object[size *
2
+
1
];
System.arraycopy(elementData,
0
, newArray,
0
, elementData.length);
/*
* for (int i = 0; i < elementData.length; i++) {
* newArray[i]=elementData[i]; }
*/
elementData = newArray;
}
elementData[size++] = obj;
// size++;
}
public void add(int index, Object obj) {
rangeCheck(index);
ensureCapacity();//数组扩容
System.arraycopy(elementData, index, elementData, index + 1, size - index);
elementData[index] = obj;
size++;
}
private void ensureCapacity() {
// 数组扩容
if (size == elementData.length) {
Object[] newArray = new Object[size * 2 + 1];
System.arraycopy(elementData, 0, newArray, 0, elementData.length);
/*
* for (int i = 0; i < elementData.length; i++) {
* newArray[i]=elementData[i]; }
*/
elementData = newArray;
}
}
public
Object get(
int
index) {
rangeCheck(index);
return
elementData[index];
}
public
void
remove(
int
index) {
rangeCheck(index);
// 删除指定位置的对象
// a b c d e
if
(index <
0
|| index >= size) {
try
{
throw
new
Exception();
}
catch
(Exception e) {
e.printStackTrace();
}
int
numMoved = size - index -
1
;
if
(numMoved >
0
) {
System.arraycopy(elementData,
index +
1
, elementData, index, numMoved);
}
elementData[--size] =
null
;
}
}
public
void
remove(Object obj) {
for
(
int
i =
0
; i < size; i++) {
if
(get(i).equals(obj)) {
// 注意：底层调用的equals方法，不是==；
remove(i);
}
}
}
public
Object set(
int
index, Object obj) {
rangeCheck(index);
Object oldValue = elementData[index];
elementData[index] = obj;
return
oldValue;
}
private
void
rangeCheck(
int
index) {
if
(index <
0
|| index >= size) {
try
{
throw
new
Exception();
}
catch
(Exception e) {
e.printStackTrace();
}
}
}
public
static
void
main(String[] args) {
My
ArrayList
slist =
new My
ArrayList(
3
);
slist.add(
132
);
slist.add(
"444"
);
slist.add(
5
);
slist.add(
"333"
);
slist.add(
"333"
);
slist.add(
"abc"
);
slist.add(
"ccc"
);
System.out.println(slist.size);
System.out.println(slist.get(
6
));
}