数据结构与算法分析Java版练习1.13

package ch01;

/**
 * 练习1.13 设计一个泛型类Collection，它存储Object对象的集合（在数组中），以及该集合的大小。提供public方法
 * isEmpty, makeEmpty, insert, remove和isPresent。方法isPresent(x)当且仅当在该集合中存在(由equals定义）
 * 等于x的一个Object时返回true。
 *
 */
class Collection<T> {
	private final static int DEFAULT_CAPACITY = 10;
	private Object[] items;
	private int size;
	public Collection() {		
		size = 0;
		ensureCapacity(DEFAULT_CAPACITY);
	}
	
	public boolean isEmpty() {
		return size == 0;
	}
	
	public void makeEmpty() {
		if (size == 0) {
			return;
		}
		
		for (int i = 0; i < size; ++i) {
			items[i] = null;
		}
		size = 0;
	}
	
	public boolean insert(T x) {
		insert(size(), x);
		return true;
	}
	
	public void insert(int idx, T x) {
		if (items.length == size())
			ensureCapacity(size() * 2 + 1);
		for (int i = size; i > idx; i--)
			items[i] = items[i - 1];
		items[idx] = x;
		size++;
	}
	
	public T remove(int idx) {
		T removedItem = (T)items[idx];
		for (int i = idx; i < size() - 1; ++i)
			items[i] = items[i+1];
		items[size() - 1] = null;
		size--;
		return removedItem;
	}
	
	public T remove(T x) {
		for (int i = 0; i < size(); ++i) {
			if (items[i].equals(x)) {
				return remove(i); 
			}
		}
		return null;
	}
	
	public boolean isPresent(T x) {
		for (int i = 0; i < size(); ++i) {
			if (items[i].equals(x)) {
				return true;
			}
		}
		return false;
	}
	
	private void ensureCapacity(int newCapacity) {
		if (newCapacity < size)
			return;
		Object[] old = items;
		items = new Object[newCapacity];
		for (int i = 0; i < size(); ++i)
			items[i] = old[i];
	}
	
	public int size() {
		return size;
	}
	
	public void display() {
		for (int i = 0; i < size(); ++i) {
			System.out.print(items[i] +" ");
		}
		//System.out.println();
	}
}
public class EX13 {
	public static void main(String[] args) {
		Collection<String> strColl = new Collection<String>();
		System.out.println("isEmpty: " + strColl.isEmpty());
		strColl.insert("a");strColl.insert("c");strColl.insert("e");
		System.out.print("After insert:" );strColl.display();
		System.out.println();
		strColl.remove("c");
		System.out.print("After remove c:"); strColl.display();
		System.out.println();
		System.out.println("if exist f: " + strColl.isPresent("f"));
		System.out.println("if exist e: " + strColl.isPresent("e"));
		strColl.makeEmpty();
		System.out.print("After make empty:");strColl.display();
		System.out.println();
	}
}