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This Java puzzle is a mystery!
By creating an object of the subclass MySub in the main method, the constructor of the superclass MySuper is called.
The constructor of MySuper invokes the method myMethod. The statement System.out.print(“-x” + m); should write -x3, because the value of m is 3.
The statement System.out.print(“-x” + n); should write -x2, because the value of n is 2.
The mystery is that this program writes -x0 to the standard output.
What is your explanation for that?
Note: The classes MySuper and MySub are two separate files in one package.
Java puzzle 3: Inheritance
Level: Hard
MySuper.java
public class MySuper { int m = 3; public MySuper() { myMethod(); } void myMethod() { System.out.print("-x" + m); } }
MySub.java
public class MySub extends MySuper { int n = 2; void myMethod() { System.out.print("-x" + n); } public static void main(String[] args) { MySub mySub = new MySub(); } }
Author: Sar Maroof
Answer explanation
- The constructor of the superclass invokes the method myMethod, which is overridden
in the subclass MySub. - The statement System.out.print(“-x” + n); in the method myMethod of
the subclass MySub writes the string “-x” and the value of the variable n
to the standard output. - The constructor of the superclass invokes the method myMethod, which is overridden in the subclass and the method tries to access the variable n inside the subclass before it is initialzied. Therefore the program writes -x0 instead of -x2 to the standard output.
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