菜鳥請教

菜鳥請教一個java的基礎麵試題。

 
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public class D
{
 public int a=10;
 public int test() { return a; }
}
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public class E extends D
{
 public int a=20;
 public int test() { return a; }
}
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Now suppose 
 
D d=new E();
 
So d.a = ? and d.test()=?
 
I understand d.test() is 20, due to inheritance finds the lowest level method and call.
But why d.a is 10?