ArrayList实现
import java.util.*; public class MyArrayList<AnyType> implements Iterable<AnyType> { private static final int DEFAULT_CAPACITY = 10; private int theSize; private AnyType[] theItems; public MyArrayList() { clear(); } public void clear() { theSize = 0; ensureCapacity(DEFAULT_CAPACITY); } public int size() { return theSize; } public boolean isEmpty() { return theSize == 0; } public void trimToSize() { ensureCapacity(size()); } public AnyType get(int idx) { if(idx < 0 || idx >= size()) throw new ArrayIndexOutOfBoundsException(); return theItems[index]; } public AnyType set(int idx, AnyType newVal) { if(idx < 0 || idx >= size()) throw new ArrayIndexOutOfBoundsException(); AnyType old = theItems[idx]; theItems[idx] = newVal; return old; } public void ensureCapacity(int newCapacity) { if(newCapacity < theSize) return; AnyType[] old = theItems; theItems = (AnyType[]) new Object[newCapacity]; for(int i = 0; i < size(); i++) theItems[i] = old[i]; } public boolean add(AnyType x) { add(size(), x); return true; } public void add(int idx, AnyType x) { if(theItems.length == size()) ensureCapacity(size() * 2 + 1); for(int i = theSize; i > idx; i--) theItems[i] = theItems[i - 1]; theItems[idx] = x; theSize++; } public AnyType remove(int idx) { if(theItems.length < idx) return; AnyType removedItem = theItems[idx]; for(int i = idx; i < size() - 1; i ++) theItems[i] = theItems[i + 1]; return removedItem; } public java.util.Iterator<AnyType> iterator() { return new ArrayListIterator(); } private class ArrayListIterator<AnyType> implements java.util.Iterator<AnyType> { private int current = 0; public boolean hasNext() { return current < size(); } public AnyType next() { if(!hasNext()) throw new java.util.NoSuchElementException(); return theItems[current++]; } public void remove() { MyArrayList.this.remove(--current); } } }