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POWhy are non-static class variables initialiized at runtime and not compile time in Java
 

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  1. POWhy are non-static class variables initialiized at runtime and not compile time in Java
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    <p>This is an extension of question: <a href="https://stackoverflow.com/questions/9865044/order-of-the-initialization-in-java/">Order of the initialization in Java</a> </p> <p>so in the code block:</p> <pre><code>public class Point { int y = getX(); int x = 42; int getX() { return x; } public static void main (String s[]) { Point p = new Point(); System.out.println(p.x + "," + p.y); } </code></pre> <p>} </p> <p>It outputs <code>42,0</code></p> <p>While the above question was answered by describing the behavior of the Java compiler and runtime, it is still bugging me why the compiler does not bake the initial value of x (42) into the bytecode? I know the values of static variables get embedded into the bytecode since they are class level variables and they dont take up any space in the object memory, but doesn't it make sense to also embed any initial values for class level non-static variables also into the bytecode? That way, the code above will be more in-line with expected behavior, and the instantiation of the object will be quicker I am guessing (since the memory assigned to x will immediately contain 42 hence saving time in parsing the initialization line in the class every time an object of class Point is created)</p> <p>I suspect this might have something to do with the tradeoffs between class bytecode size, object initialization efficiency, and compile time efficiency.</p> <p>I am hoping someone with deep knowledge on Java compiler/runtime can throw some light on this. Knowing how a framework works internally always helps us write better code :-)</p>
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    1. USVijay Agrawal
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    1. COWould it not create problems if the variable was an object? It's all fine and good when the value is 42 but what if the value is an object of class ComplexNumber? Do we want all our points to refer to the same memory address and, essentially, the same ComplexNumber? Now I am not someone with deep knowledge of Java compiler/runtime stuff so I could be totally wrong here but that's the best reason I can come up with.
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    2. COIt *does* 'bake the initial value of x (42) into the bytecode'. How do you think x ever gets to be 42? It doesn't bake it into the *instance memory,* because there *is no* instance memory, until you create an instance. At runtime. Your question doesn't make sense.
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