非public类中的public方法有什么作用

package com.jaeson.javastudy.effectivejava;
public abstract class PublicMethodInNonPublicClass {

	public static PublicMethodInNonPublicClass getInstance() {
		return new NonPublicClass();
	}
	public abstract void show();
}

class NonPublicClass extends PublicMethodInNonPublicClass {
	@Override public void show() {
		System.out.println("NonPublicClass.show is calling...");
	}
}

/////////////////////////////////////////////////////////////////
package com.jaeson.javastudy;

import com.jaeson.javastudy.effectivejava.*;

public class TestNonPublicClass {

	public static void main(String[] args) {
		PublicMethodInNonPublicClass npc = PublicMethodInNonPublicClass.getInstance();
		npc.show();
		//wrong:NonPublicClass is not visible
		//new NonPublicClass();
	}
}

 

 * 可以隐藏类的实现细节，只对外提供接口，客户端无法通过import直接构建具体类的实例。