1. Memory leaks in Java? Not exactly memory leak
but reduced performance due to
increased garbage collection activities and
increased memory footprint
Good Java Programming
8/23/2018

2. Stack implementation in Java
public class MyStack {
private Object[] stackElements;
private int currentSize = 0;
private static int INIT_CAPACITY = 100;
public MyStack() {
stackElements = new Object[INIT_CAPACITY]; }
public void push(Object objAdd) {
ensureCapacity();
currentSize++;
stackElements[currentSize] = objAdd;
// code continued in next slide
Good Java Programming
8/23/2018

3. Stack implementation in Java (contd)
public Object pop() {
if (0 == currentSize)
throw new EmptyStackException();
currentSize--;
return stackElements[currentSize]; }
private void ensureCapacity() {
if (stackElements.length == currentSize) {
// double the array + 1
// copyOf method:
stackElements = Arrays.copyOf(stackElements, 2 * currentSize + 1);
} // end class MyStack
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8/23/2018

4. Memory leaks in Java?
As the stack grows and shrinks objects that were popped off will not be garbage collected
even if the driver/client code, which is using the Stack, does not have those references
Why?
Stack maintains obsolete references to these objects
Obsolete reference: a reference that will never be dereferenced again
This is called Unintentional Object Retention
Note that such objects may contain other references and so on
Good Java Programming
8/23/2018

5. Unintentional Object Retention
Note that such objects may contain other references and so on
Guideline
Always null the references
Added benefit
accidental use of that reference (array index in this case) will result in a NullPointerException
Do NOT null every reference
overkill, cluttered code
Define each variable in the narrowest possible scope and let it fall out of scope (we will discuss this later)
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8/23/2018

6. Eliminate obsolete references
public Object pop() {
if (0 == currentSize)
throw new EmptyStackException();
Object resultObj = stackElements[currentSize];
// elimnate the obsolete reference by setting it to null
stackElements[currentSize] = null;
currentSize--;
return resultObj; }
Good Java Programming
8/23/2018

7. Design Guideline Eliminate obsolete object references
Good Java Programming
8/23/2018