Null Object模式

在程序中经常要使用==null来判定对象是否初始化，可以采用null object模式来简化这样的代码，从而提高健壮性。

/**
 * 
 */

/**
 * @author lucy
 * 
 */
public abstract class AbstractProduct {
	public String name;
	public Integer price;
	private static AbstractProduct nullProduct = null;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Integer getPrice() {
		return price;
	}

	public void setPrice(Integer price) {
		this.price = price;
	}

	public static AbstractProduct getNullProduct() {
		if (AbstractProduct.nullProduct == null) {
			return new NullProduct();
		}
		return nullProduct;
	}

}

public class NullProduct extends AbstractProduct {
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Integer getPrice() {
		return price;
	}

	public void setPrice(Integer price) {
		this.price = price;
	}

	public boolean isNull() {
		return true;
	}

}

public class Product extends AbstractProduct {
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Integer getPrice() {
		return price;
	}

	public void setPrice(Integer price) {
		this.price = price;
	}

	public boolean isNull() {
		return false;
	}
}