2018-09-27模拟ArrayList底层实现、
1.模拟ArrayList底层实现：
public class MyArrayList {
StringBuilder s;//防照StringBuilder
ArrayList a;//在查看Arraylist的一些简单方法
/**
* The value is used for Object storage.
*/
private Object[] value;
/**
* The size is the number of Objects used.
*/
private int size;
public MyArrayList(){
//value = new Object[16];
this(10);
}
/**
* Creates an MyArrayList of the specified capacity
* 指定容量
*/
public MyArrayList(int size){
if(size < 0){
try {
throw new Exception();
} catch (Exception e) {
e.printStackTrace();
}
}
value = new Object[size];
}
public void add(Object obj){
value[size] = obj;
size++;
if(size >= value.length){
//默认为10，大了的时候需要扩容
int newCapacity = value.length * 2;
Object[] newList = new Object[newCapacity];
// System.arraycopy(src, srcPos, dest, destPos, length);
for(int i = 0;i < value.length;i++){
newList[i] = value[i];
}
value = newList;
}
}
public Object get(int index){
if(index < 0 || index > size-1){
try {
throw new Exception();
} catch (Exception e) {
e.printStackTrace();
}
}
return value[index];
}
public int size(){
return size;
}
public boolean isEmpty() {
return size == 0;
}
public boolean contains(Object o){
return Indexof(o) >= 0;
}
private int Indexof(Object o) {
if(o == null){
for(int i = 0; i < size; i++)
if(value[i] == null)
return i;
}else{
for (int i = 0; i < size; i++)
if (o.equals(value[i]))
return i;
}
return -1;
}
//从头开始检索
public int indexOf(Object o){
if(o == null){
for(int i = 0; i < size; i++){
if(value[i]==null)
return i;
}
}else{
for(int i =0;i < size; i++){
if(o.equals(value[i]))
return i;
}
}
return -1;
}
public int lastIndexOf(Object o){
if(o == null){
for(int i = size - 1; i >= 0; i--){
if(value[i]==null)
return i;
}
}else {
for(int i = size-1;i >= 0; i--){
if(o.equals(value[i]))
return i;
}
}
return -1;
}
public static void main(String[] args) {
MyArrayList myList = new MyArrayList(2);//初始化为16，所以超过是应当去扩容
myList.add("1");
myList.add(2);
myList.add(3);
myList.add(2);
myList.add(3);
myList.add(2);
myList.add(3);
System.out.println(myList.get(0));//1
System.out.println(myList.size);//7
System.out.println(myList.isEmpty());//false
System.out.println(myList.contains(null));//false
System.out.println(myList.lastIndexOf(3));//6
}
}
