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javapermgen

PermGen space of heap

As shown in the image, Permgen is further divided into several parts.

enter image description here

Runtime constant pool stores constants pertaining to each type that is loaded by class loader.

Method area stores method information such as method return type, method name. (correct me if I am wrong here.)

And Reserved area is the part which is reserved if more memory is required by permgen.

But what I don't understand is, what is code area in the image? Any code is stored in this space(seems vague to me)?

Solution 
  • Any code is stored in this space(seems vague to me)?

    Any specific reason for that ?

    The possible answer could be : Code area stores the byte code of the classes loaded into your memory.

    But then the question comes, Why class is not loaded directly in RAM ?

    Because we have a JVM to provide interoperability, Since JVM is an intermediary between java code and the machine , we need some place to store the code statements until JVM is scheduled by OS to execute its code.(for OS JVM is a process). So, It loads the byte code in Code area(if i am right) and when scheduled, further interprets code(.class) into underlying machine instructions.

    The answer to me is "Code area holds the byte code of the classes".

    To back the idea mentioned above ., here are some concepts copied as it is from Oracle blog which says:

    So the Java classes are stored in the permanent generation. What all does that entail? Besides the basic fields of a Java class there are:

    1. Methods of a class (including the bytecodes)
    2. Names of the classes (in the form of an object that points to a string also in the permanent generation)
    3. Constant pool information (data read from the class file, see chapter 4 of the JVM specification for all the details).
    4. Object arrays and type arrays associated with a class (e.g., an object array containing references to methods).
    5. Internal objects created by the JVM (java/lang/Object or java/lang/exception for instance)
    6. Information used for optimization by the compilers (JITs)

    Hope it clears.