person类与其子类在使用中的内存情况_Java

public class Person
{
	public String xm;
	public int nl;
	public void setme(String x,int y)
	{
		xm=x;
		nl=y;
	}
	public void showme()
	{
		System.out.println("我是"+xm+",今年"+nl+"岁");
	}
}
public static void main(String[] args)
	{
		// TODO Auto-generated method stub
		Person a,b;
		a=new Person();
		b=new Person();
		a.setme("张三",20);
		b.setme("李四",18);
		a.showme();
		b.showme();
	}

public class Person1 extends Person
{
	public void showme()
	{
		System.out.println("我是中国人"+xm+",今年"+nl+"岁");
	}
}

public static void main(String[] args)
	{
		// TODO Auto-generated method stub
		Person1 a;
		Person b,c;
		a=new Person1();
		b=new Person();
		a.setme("张三",20);
		b.setme("李四",18);
		c=a;
		a.showme();
		b.showme();
		c.showme();
	}