我正在尝试在代码下方运行，但出现类型转换错误，当它从 main 获取输入时，它不会评估并给我给定错误。
谁能给我一些我做错的信息..
Expression (+ (- 6) (* 2 3 4) (/ (+ 3) (- 2 3 1)))
Expr in thread "main" java.lang.NumberFormatException: For input string: "(+ (- 6)
(* 2 3 4) (/ (+ 3) (* 1) (- 2 3 1)))"
at sun.misc.FloatingDecimal.readJavaFormatException: For input string "(+ (- 6) (* 2 3
4) (/ (+ 3) (* 1) (- 2 3 1)))"
at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
我的代码：
public class SimpleLispExpressionEvaluator
{
// Current input Lisp expression
private String inputExpr;
// Main expression stack & current operation stack, see algorithm in evaluate()
// Use StackInterface
private StackInterface<Object> exprStack;
private StackInterface<Double> currentOpStack;
// default constructor
// set inputExpr to ""
// create stack objects
public SimpleLispExpressionEvaluator()
{
// add statements
inputExpr = "";
expressionStack = new Stack<Object>();
currentOpStack = new Stack<Double>();
}
// default constructor
// set inputExpr to inputExpression
// create stack objects
public SimpleLispExpressionEvaluator(String inputExpression)
{
// add statements
inputExpr = inputExpression;
expressionStack = new Stack<Object>();
currentOpStack = new Stack<Double>();
}
// set inputExpr to inputExpression
// clear stack objects
public void reset(String inputExpression)
{
// add statements
inputExpr = inputExpression;
Stack<Object> expressionStack = new Stack<Object>();
Stack<Double> currentOpStack = new Stack<Double>();
}
private boolean checkifNumber() {
return false;
}
// This function evaluate current operator with its operands
// See complete algorithm in evaluate()
//
// Main Steps:
// Pop operands from exprStack and push them onto
// currentOpStack until you find an operator
// Apply the operator to the operands on currentOpStack
// Push the result into exprStack
//
private double add() {
double op1 = currentOpStack.pop();
double op2 = currentOpStack.pop();
double temp = op1 + op2;
return temp;
}`
private double multiply() {
double op1 = currentOpStack.pop();
double op2 = currentOpStack.pop();
double temp = op1 * op2;
return temp;
}
private double subtract() {
if (currentOpStack.size() == 1) {
double temp = -currentOpStack.pop();
return temp;
} else {
double op1 = currentOpStack.pop();
double op2 = currentOpStack.pop();
double temp = op1 - op2;
return temp;
}
}
private double divide() {
if (currentOpStack.size() == 1) {
double temp = 1 / currentOpStack.pop();
return temp;
} else if (currentOpStack.pop() == 0 || currentOpStack.pop() == null)
{
throw new IndexOutOfBoundsException(); } else {
double op1 = currentOpStack.pop();
double op2 = currentOpStack.pop();
double temp = op1 - op2;
return temp;
}
}
private void evaluateCurrentOperation()
{
// add statements
while( expressionStack.peek().getClass().getName().equals("java.lang.Double") ) {
currentOpStack.push( (Double)expressionStack.pop() );
}
Character operator = (Character)expressionStack.pop();
Double result = null;
switch( operator ) {
case '+':
result = add();
break;
case '*':
result = multiply();
break;
case '-':
result = subtract();
break;
case '/':
result = divide();
break;
}
expressionStack.push( result );
}
/**
* This function evaluates current Lisp expression in inputExpr
* It return result of the expression
*
* The algorithm:
*
* Step 1 Scan the tokens in the string.
* Step 2 If you see an operand, push operand object onto the exprStack
* Step 3 If you see "(", next token should be an operator
* Step 4 If you see an operator, push operator object onto the exprStack
* Step 5 If you see ")" // steps in evaluateCurrentOperation() :
* Step 6 Pop operands and push them onto currentOpStack
* until you find an operator
* Step 7 Apply the operator to the operands on currentOpStack
* Step 8 Push the result into exprStack
* Step 9 If you run out of tokens, the value on the top of exprStack is
* is the result of the expression.
*/
public double evaluate()
{
// only outline is given...
// you need to add statements/local variables
// you may delete or modify any statements in this method
// use scanner to tokenize inputExpr
Scanner inputExprScanner = new Scanner(inputExpr);
// Use zero or more white space as delimiter,
// which breaks the string into single character tokens
inputExprScanner = inputExprScanner.useDelimiter("\\s*");
// Step 1: Scan the tokens in the string.
while (inputExprScanner.hasNext())
{
// Step 2: If you see an operand, push operand object onto the exprStack
if (inputExprScanner.hasNextInt())
{
// This force scanner to grab all of the digits
// Otherwise, it will just get one char
String dataString = inputExprScanner.findInLine("\\d+");
expressionStack.push(new Double(dataString));
// more ...
}
else
{
// Get next token, only one char in string token
String aToken = inputExprScanner.next();
char item = aToken.charAt(0);
String nextToken;
char nextItem;
switch (item)
{
case '(':
nextToken = inputExprScanner.next();
nextItem = nextToken.charAt(0);
if (nextItem == '+') {
expressionStack.push(nextItem);
} else if (nextItem == '-') {
expressionStack.push(nextItem);
} else if (nextItem == '*') {
expressionStack.push(nextItem);
} else {
expressionStack.push(nextItem);
}
break;
case ')':
try {
evaluateCurrentOperation();
} catch (EmptyStackException e) {
break;
}
break;
default: // error
throw new RuntimeException(item + " is not a legal expression operator");
} // end switch
} // end else
} // end while
// Step 9: If you run out of tokens, the value on the top of expressionStack is
// is the result of the expression.
//
// return result
double result = new Double(inputExpr);
return result;
}
// This static method is used by main() only
private static void evaluateExprTest(String s, SimpleLispExpressionEvaluator expr)
{
Double result;
System.out.println("Expression " + s);
expr.reset(s);
result = expr.evaluate();
System.out.printf("Result %.2f\n", result);
System.out.println("-----------------------------");
}
public static void main (String args[])
{
SimpleLispExpressionEvaluator expr= new SimpleLispExpressionEvaluator();
String test1 = "(+ (- 6) (* 2 3 4) (/ (+ 3) (* 1) (- 2 3 1)))";
String test2 = "(+ (- 632) (* 21 3 4) (/ (+ 32) (* 1) (- 21 3 1)))";
String test3 = "(+ (/ 2) (* 2) (/ (+ 1) (+ 1) (- 2 1 )))";
String test4 = "(+ (/2))";
String test5 = "(+ (/2 3 0))";
String test6 = "(+ (/ 2) (* 2) (/ (+ 1) (+ 3) (- 2 1 ))))";
evaluateExprTest(test1, expr);
evaluateExprTest(test2, expr);
evaluateExprTest(test3, expr);
evaluateExprTest(test4, expr);
evaluateExprTest(test5, expr);
evaluateExprTest(test6, expr);
}
}