returnstatementnode.java

是有关解释器的.用JAVA编写.可以解释一般的JAVA程序.

/**
 * Class representing a return statement *
 */

class ReturnStatementNode extends ExecutableNode
{
	ExpressionNode vExpressionNode;
	Value vExpressionValue;
	
    static ReturnStatementNode parserReturnStatement(Environment env, Scanner s) throws ParserException, ScannerException
    {
    	ExpressionNode tmpExpressionNode=null;
    	
        matchKeyword(s, "return");
        if(!isSimpleToken(s,';'))
        	tmpExpressionNode= ExpressionNode.parserExpression(env,s); 
        matchSimple(s, ';');
 
        return new ReturnStatementNode(tmpExpressionNode); 
    }
    static boolean mIsReturnStatement(Scanner s) throws ScannerException
	{
    	return isKeywordToken(s,"return");
	}
    ReturnStatementNode()
    {
    	vExpressionNode= null;
    }
    ReturnStatementNode(ExpressionNode aExpressionNode)
	{
    	vExpressionNode= aExpressionNode;
	}
    
    Environment run(Environment env) throws InterpreterException
    {    	    	            	    	   
    	ProgramNode.vTopLevelEnvironment.put("returnValue", vExpressionValue);    
    	BlockNode.vReturn= true;
    	
    	return env;
    }

    String format(int indent)
    {
    	String str="";
    	if(vExpressionNode!=null)str= vExpressionNode.format(indent);
        return space(indent) + "return "+str+";\n";
    }
    boolean typeCheck(Environment env) throws InterpreterException
	{    
    	Object resultType= ProgramNode.vTopLevelEnvironment.get("returnType");
    	
    	if(resultType.toString().equals("void"))
    		if(vExpressionNode!=null)ProgramNode.mTypeCheckError(this.format(4) + " mustn't exist in a void method");
    			else return true;
    	else
    	{
    		if(vExpressionNode.typeCheck(env))
    		{    			
    			vExpressionValue= vExpressionNode.evaluate(env);
    			if(vExpressionValue.isOfType(resultType.toString()))return true;
    				else ProgramNode.mTypeCheckError(this.format(4) + "  isn't match the type of the method");
    		}else ProgramNode.mTypeCheckError(vExpressionNode.format(4));
    	} 	
    				
    	return false;
	}
}