Java Memory Structure | Chang Min Park

types of memory area

memory21

Static memory (Method area)

Method information and Field information.
Global constants and other data generated by the compiler(e.g. info to support garbage collection) are allocated static storage.
Static variables are bound to memory cells before execution begins and remains bound to the same memory cell throughout execution. E.g., static variables.

Stack

Names local to a procedure and Parameters are allocated space on a stack. The size of stack can not be determined at compile time.

Heap

Data that may outlive the call to the procedure that created it is usually allocated on a heap. E.g. new to create objects that may be passed from procedure to procedure.
The size of heap can not be determined at compile time. Referenced only through pointers or references, e.g., dynamic objects in C++, all objects in Java
Garbage collection cleans up data(not using) on heap.

Example

class Point {
   int x, y;

   void move(int x, int y) {
      this.x = x;
      this.y = y;
   }

   int getX() {
      return x;
   }

   int getY() {
      return y;
   }

   void setX(int x) {
      this.x = x;
   }

   void setY(int y) {
      this.y = y;
   }

   void draw() {
      System.out.println("Point(" + x + ", " + y + ")");
   }
}

class PointTest {
   public static void main(String args[]) {
      Point p1, p2 = null;

      p1 = new Point();
      p1.move(4, 4);
      // Point 1
      p2 = new Point();
      p2.move(2, 4);

      // Point 2
   }
}

[ PointTest class loaded ]