自定义MyArrayList

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public class MyArrayList<AnyType> implements Iterable<AnyType> {
@Override
public Iterator<AnyType> iterator() {
return new ArrayListIterator();
}
}
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private static final int DEFAULT_CAPACITY = 10;
private int theSize;
private AnyType[] theArrays;
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public MyArrayList(){
theArrays = (AnyType[])new Object[DEFAULT_CAPACITY];
doClear();
}
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private void doClear(){
theSize = 0;
expandCapacity(DEFAULT_CAPACITY);
}
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public void expandCapacity(int newCapacity){
if (newCapacity < theSize){
return;
}
// 数组容量的扩充:
AnyType[] newArrays = (AnyType[])new Object[newCapacity];
// 利用 System.arraycopy() 方法拷贝数组
System.arraycopy(theArrays,0,newArrays,0,theSize);
theArrays = newArrays;
}
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/**
* 根据下标得到数组元素的值
*/
public AnyType get(int idx){
if (idx <0 || idx >= theSize){
throw new ArrayIndexOutOfBoundsException();
}
return theArrays[idx];
}
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/**
* 根据下标设置数组元素的值
* 返回该下标元素的原值
*/
public AnyType set(int idx,AnyType newVal){
if (idx <0 || idx >= theSize){
throw new ArrayIndexOutOfBoundsException();
}
AnyType oldVal = theArrays[idx];
theArrays[idx] = newVal;
return oldVal;
}
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 /**
* 根据下标向数组插入新元素
*/
public boolean add(int idx,AnyType newVal){
// 当 idx=theSize 时，在 A[theSize] 位置处插入元素
if (idx < 0 || idx > theSize){
throw new ArrayIndexOutOfBoundsException();
}
// 数组满时扩充容量
if (theArrays.length == theSize){
expandCapacity(theSize*2 + 1);
}
// 数组元素后移
for (int i=theSize;i>idx;i--){
theArrays[i] = theArrays[i-1];
}
theArrays[idx] = newVal;
theSize++;
return true;
}
/**
* 在数组末尾插入新元素
*/
public boolean add(AnyType newVal){
add(theSize,newVal);
return true;
}
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/**
* 根据下标删除元素
* 返回被删除的元素
*/
public AnyType remove(int idx){
if (idx < 0 || idx >= theSize){
throw new ArrayIndexOutOfBoundsException();
}
// 数组元素前移
AnyType removedElem = theArrays[idx];
for (int i = idx; i < theSize-1; i++) {
theArrays[i] = theArrays[i+1];
}
theSize--;
return removedElem;
}
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public interface Iterator<AnyType> {
boolean hasNext();
AnyType next();
void remove();
}
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public static <AnyType> void print(Collection<AnyType> coll){
Iterator<AnyType> itr = coll.iterator();
while(itr.hasNext()){
AnyType item = itr.next();
System.out.println(item);
// itr.remove();
}
}
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import java.util.Iterator;
import java.util.NoSuchElementException;
public class MyArrayList<AnyType> implements Iterable<AnyType> {
......
@Override
public Iterator<AnyType> iterator() {
return new ArrayListIterator();
}
private class ArrayListIterator implements Iterator<AnyType>{
// 初始时当前位置为 0
private int current = 0;
@Override
public boolean hasNext() {
return current < theSize;
}
@Override
public AnyType next() {
if (!hasNext()){
throw new NoSuchElementException();
}
return theArrays[current++];
}
@Override
public void remove() {
/* 因为 remove() 方法有相同的，MyArrayList.this 表示外部类当前对象的一个引用 */
MyArrayList.this.remove(--current);
}
}
}
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