The WeakReference class, monitoring memory leak and garbage collection in a Java application

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 Below is a Stack implementation that uses an internal resizeable array structure.  public class MyStack< T > implements Stack< T > { private static final int CAPACITY = 100 ; private Object[] array ; private int pos = 0 ; public MyStack () { this . array = new Object[ CAPACITY ] ; } @Override public void push ( T item) { if ( pos >= array . length / 2 ) { Object[] newArray = new Object[ pos * 2 ] ; System. arraycopy ( array , 0 , newArray , 0 , array . length ) ; array = newArray ; } array [ pos ++] = item ; } @Override public T pop () { if (isEmpty()) { throw new RuntimeException( "empty stack" ) ; } @SuppressWarnings ( "unchecked" ) T item = ( T ) array [ pos - 1 ] ; pos -= 1 ; return item ; } @Override @SuppressWarnings ( "unchecked" ) public T peek...
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A Code Analyzer for a Subset of Java Language (J-) Using ANTLR - PART 2

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As we know, semantic analysis of a compiler includes checking the types of expressions.
To do that, we have to maintain a Symbol Table which maps variable names to their types and locations. There maybe many variables with the same name which are in different scopes. This is legal in most languages and we have to handle this situation.

We have to know when following scopes are entered in:
- class scope
- method scope
- no inner block scopes (my language does not support this currently)

We will do type-checking in two phases. First we'll populate the Symbol Table and it will contain the symbols with their scopes. Then, we'll check the types of symbols that are subject to addition operation by querying the symbol table.

ANTLR allows us to inject code in different places of the generated parser. We need to know when a class/method scope is entered and the end of any scope is reached. Below is some grammar code from the project:


classDecl
@init {visitor.beforeClass(); System.out.println("class classScope started");}
@after {visitor.afterClass(); System.out.println("class classScope ended");}
: ^(CLASS ID varDecl* methodDecl*) {visitor.onClassName($ID.text); System.out.println("class is: " + $ID.text);}
;

methodDecl
@init {visitor.beforeMethod(); System.out.println("method classScope started");}
@after {visitor.afterMethod(); System.out.println("method classScope ended");}
: ^(METHOD type ID formalParameter* block) {visitor.onMethodName($ID.text);}
;

We inject a visitor to the parser because we don't want to clutter the tree grammar code with type-checking details.

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