C14 空对象

Null对象的设计

/**
 * 
 * @author Rock Lee
 * @Description 标记接口
 */
public interface Null {

}

/**
 * 
 * @author Rock Lee
 * @Description 
 */
public class Person {
	private String first;
	private String last;
	private String address;
	public static final Person NULL  = new NullPerson();

	public Person() {
		super();
	}

	public Person(String first, String last, String address) {
		super();
		this.first = first;
		this.last = last;
		this.address = address;
	}
	/**
	 * 
	 * @author Rock Lee
	 * @Description 内部类 对标记接口实现
	 */
	public static class NullPerson extends Person implements Null {
		private NullPerson() {
			super("None", "None", "None");
		}

		@Override
		public String toString() {
			return "NullPerson";
		}
	}

	@Override
	public String toString() {
		return "Person [first=" + first + ", last=" + last + ", address="
				+ address + "]";
	}

}

public class TestNullObject {
	@Test
	public void test(){
		Person p = Person.NULL;
		System.out.println(p);
	}
}