java dynamic memory allocation

advertisements

I've been learning Java for almost a year, but still feel confused when it comes to dynamic memory allocation.

Question 1: Can anyone elaborate what happens in memory when below code get executed based on the steps I wrote (Please correct me if I was wrong)? The more detailed the better.

Question 2: What kind of book/website should I read/visit if I want to dig deeper into JVM or Java memory?

class Student {
  private static int counter;
  private String name;
  private int age;
  private String grade = "grade 1";

  Student(String _name, int _age) {
     this.name = _name;
     this.age = _age;
  }

  public static void main(String[] args){
     Student s = new Student("Emma", 6);
  }
}

  1. Student.classfile get loaded, static variablecounterare initialized on data area.
  2. main()get called, JVM allocates memory on stack for local variables.
  3. JVM allocates storage for member variablesname,ageandgradeon heap, and zeros the storage.
  4. gradeget initialized as"grade 1".
  5. constructorStudent()get called to initialize the new instance: JVM allocates memory for_nameand_ageon stack, initialize them to"Emma"and6, then copy their values to member variablesnameandage.
  6. JVM assign this new instance tos.

You have 4 and 5 out of order. Constructors first call super() in one form or another, then all initializers and anonymous init blocks, in textual order, then their own body after thesuper() call if any. You also have the allocation and initialization of _name and _age in the wrong place: it happens before the constructor is called. See the JLS and JVM Specification for details.