C 語言程序變數作用域的實現機制是什麼？

/**
* 用於對抽象語法樹(AST)中每個結點訪問的抽象類 針對不同的處理階段，生成不同的子類， 比如：進行類型檢查的TypeCheckingVisitor。
* 而針對每一種類型的樹結點，都有相應的visit方法的重載形式。
*
* @author Jian p Zeng.
* @version 1.0
*/
public abstract class Visitor
{
/**
* A generic visitor class for trees.
*/

public Visitor()
{
super();
}

/**
* A method visits topLevel tree node.
* @param that
*/
public void visitTopLevel(TopLevel that)
{
visitTree(that);
}

/**
* A method visits import declaration tree node.
* @param that
*/
public void visitImport(Import that)
{
visitTree(that);
}

/**
* A method visits Class and interface definition tree node.
* @param that
*/
public void visitClassDef(ClassDef that)
{
visitTree(that);
}

/**
* A method visits method declaration tree node.
* @param that
*/
public void visitMethodDef(MethodDef that)
{
visitTree(that);
}

/**
* A method visits variable definition tree node.
* @param that
*/
public void visitVarDef(VarDef that)
{
visitTree(that);
}

/**
* Skips no-op statements.
* @param that
*/
public void visitSkip(Skip that)
{
visitTree(that);
}

/**
* A method visits Block statements tree node.
* @param that
*/
public void visitBlock(Block that)
{
visitTree(that);
}

/**
* A method visits do while loop tree node.
* @param that
*/
public void visitDoLoop(DoLoop that)
{
visitTree(that);
}

/**
* A method visits while loop tree node.
* @param that
*/
public void visitWhileLoop(WhileLoop that)
{
visitTree(that);
}

/**
* A method visits for loop tree node.
* @param that
*/
public void visitForLoop(ForLoop that)
{
visitTree(that);
}

/**
* A method visits labeled statement tree node.
* @param that
*/
public void visitLabelled(Labelled that)
{
visitTree(that);
}

/**
* A method visits switch statement tree node.
* @param that
*/
public void visitSwitch(Switch that)
{
visitTree(that);
}

/**
* A method visits case statement of switch tree node.
* @param that
*/
public void visitCase(Case that)
{
visitTree(that);
}

/**
* A method visits synchronize block tree node.
* @param that
*/
public void visitSynchronized(Synchronized that)
{
visitTree(that);
}

/**
* A method visits try tree node.
* @param that
*/
public void visitTry(Try that)
{
visitTree(that);
}

/**
* A method visits catch tree node.
* @param that
*/
public void visitCatch(Catch that)
{
visitTree(that);
}

public void visitConditional(Conditional that)
{
visitTree(that);
}

public void visitIf(If that)
{
visitTree(that);
}

public void visitExec(Exec that)
{
visitTree(that);
}

public void visitBreak(Break that)
{
visitTree(that);
}

public void visitContinue(Continue that)
{
visitTree(that);
}

public void visitReturn(Return that)
{
visitTree(that);
}

public void visitThrow(Throw that)
{
visitTree(that);
}

public void visitAssert(Assert that)
{
visitTree(that);
}

public void visitApply(Apply that)
{
visitTree(that);
}

public void visitNewClass(NewClass that)
{
visitTree(that);
}

public void visitNewArray(NewArray that)
{
visitTree(that);
}

public void visitParens(Parens that)
{
visitTree(that);
}

public void visitAssign(Assign that)
{
visitTree(that);
}

public void visitAssignop(Assignop that)
{
visitTree(that);
}

public void visitUnary(Unary that)
{
visitTree(that);
}

public void visitBinary(Binary that)
{
visitTree(that);
}

public void visitTypeCast(TypeCast that)
{
visitTree(that);
}

public void visitTypeTest(TypeTest that)
{
visitTree(that);
}

public void visitIndexed(Indexed that)
{
visitTree(that);
}

public void visitSelect(Select that)
{
visitTree(that);
}

public void visitIdent(Ident that)
{
visitTree(that);
}

public void visitLiteral(Literal that)
{
visitTree(that);
}

public void visitTypeIdent(TypeIdent that)
{
visitTree(that);
}

public void visitTypeArray(TypeArray that)
{
visitTree(that);
}

public void visitErroneous(Erroneous that)
{
visitTree(that);
}

public void visitTree(Tree that)
{
assert false;
}