我目前正在我的学校参加AP计算机科学课程，我的一个项目遇到了一些麻烦！该项目要求我创建一个计算器，可以评估表达式然后解决它。我已经完成了大部分工作，但我遇到了一点麻烦，因为我的老师让我使用while循环来不断询问输入并显示答案，我坚持这一点。要结束程序，用户必须键入“退出”，我不能使用system.exit（）或任何作弊的东西，程序必须用完代码。我的大部分内容也是如此，但我无法找到return方法expression中的MethodToReadInput();为什么有人提出任何提示？
import java.util.*;
public class Calculator {
public static void main(String[] args) {
System.out.println("Welcome to the AP Computer Science calculator!!");
System.out.println();
System.out.println("Please use the following format in your expressions: (double)(space)(+,-,*,/...)(space)(double)");
System.out.println("or: (symbol)(space)(double)");
System.out.println();
MethodToReadInput();
MethodToTestInput(MethodToReadInput());
}
public static String MethodToReadInput() {
Scanner kb = new Scanner(System.in);
System.out.print("Enter an expression, or quit to exit: ");
String expression = kb.nextLine();
if (expression.equalsIgnoreCase("quit")) {
System.out.println("Goodbye!");
}
else {
return expression;
}
}
public static void MethodToTestInput(String expression) {
while (!expression.equalsIgnoreCase("quit")) {
MethodToReadInput();
MethodtoEvaluateInput(expression);
}
System.out.println("Goodbye!");
}
public static void MethodtoEvaluateInput(String expression) {
if (OperatorFor2OperandExpressions(expression).equals("+")) {
System.out.println(FirstOperandFor2OperandExpressions(expression) + " " + OperatorFor2OperandExpressions(expression) + " " + SecondOperandFor2OperandExpressions(expression) + " = " + (FirstOperandFor2OperandExpressions(expression) + SecondOperandFor2OperandExpressions(expression)));
}
else if (OperatorFor2OperandExpressions(expression).equals("*")) {
System.out.println(FirstOperandFor2OperandExpressions(expression) + " " + OperatorFor2OperandExpressions(expression) + " " + SecondOperandFor2OperandExpressions(expression) + " = " + (FirstOperandFor2OperandExpressions(expression) * SecondOperandFor2OperandExpressions(expression)));
}
else if (OperatorFor2OperandExpressions(expression).equals("-")) {
System.out.println(FirstOperandFor2OperandExpressions(expression) + " " + OperatorFor2OperandExpressions(expression) + " " + SecondOperandFor2OperandExpressions(expression) + " = " + (FirstOperandFor2OperandExpressions(expression) - SecondOperandFor2OperandExpressions(expression)));
}
else if (OperatorFor2OperandExpressions(expression).equals("/")) {
System.out.println(FirstOperandFor2OperandExpressions(expression) + " " + OperatorFor2OperandExpressions(expression) + " " + SecondOperandFor2OperandExpressions(expression) + " = " + (FirstOperandFor2OperandExpressions(expression) / SecondOperandFor2OperandExpressions(expression)));
}
else if (OperatorFor2OperandExpressions(expression).equals("^")) {
System.out.println(FirstOperandFor2OperandExpressions(expression) + " " + OperatorFor2OperandExpressions(expression) + " " + SecondOperandFor2OperandExpressions(expression) + " = " + Math.pow(FirstOperandFor2OperandExpressions(expression),SecondOperandFor2OperandExpressions(expression)));
}
else if (OperatorFor1OperandExpressions(expression).equals("|")) {
System.out.println(OperatorFor1OperandExpressions(expression) + " " + OperandFor1OperatorExpressions(expression) + " = " + Math.abs(OperandFor1OperatorExpressions(expression)));
}
else if (OperatorFor1OperandExpressions(expression).equals("v")) {
System.out.println(OperatorFor1OperandExpressions(expression) + " " + OperandFor1OperatorExpressions(expression) + " = " + Math.sqrt(OperandFor1OperatorExpressions(expression)));
}
else if (OperatorFor1OperandExpressions(expression).equals("~")) {
double x = 0.0;
System.out.println(OperatorFor1OperandExpressions(expression) + " " + OperandFor1OperatorExpressions(expression) + " = " + (Math.round(OperandFor1OperatorExpressions(expression))+ x));
}
else if (OperatorFor1OperandExpressions(expression).equals("s")) {
System.out.println(OperatorFor1OperandExpressions(expression) + " " + OperandFor1OperatorExpressions(expression) + " = " + Math.sin(OperandFor1OperatorExpressions(expression)));
}
else if (OperatorFor1OperandExpressions(expression).equals("c")) {
System.out.println(OperatorFor1OperandExpressions(expression) + " " + OperandFor1OperatorExpressions(expression) + " = " + Math.cos(OperandFor1OperatorExpressions(expression)));
}
else if (OperatorFor1OperandExpressions(expression).equals("t")) {
System.out.println(OperatorFor1OperandExpressions(expression) + " " + OperandFor1OperatorExpressions(expression) + " = " + Math.tan(OperandFor1OperatorExpressions(expression)));
}
}
public static double FirstOperandFor2OperandExpressions(String expression) {
String[] tokens = expression.split(" ");
String OperandOrOperator = tokens[0];
double y = Double.parseDouble(OperandOrOperator);
return y;
}
public static double SecondOperandFor2OperandExpressions(String expression) {
String[] tokens = expression.split(" ");
String OperandOrOperator = tokens[2];
double y = Double.parseDouble(OperandOrOperator);
return y;
}
public static String OperatorFor2OperandExpressions(String expression) {
String[] tokens = expression.split(" ");
String OperandOrOperator = tokens[1];
return OperandOrOperator;
}
public static String OperatorFor1OperandExpressions(String expression) {
String[] tokens = expression.split(" ");
String OperandOrOperator = tokens[0];
return OperandOrOperator;
}
public static double OperandFor1OperatorExpressions(String expression) {
String[] tokens = expression.split(" ");
String OperandOrOperator = tokens[1];
double y = Double.parseDouble(OperandOrOperator);
return y;
}
}
答案 0 :(得分：1)
您需要将MethodToReadInput和MethodtoEvaluateInput放在循环中。例如：
public static void main(String[] args)
{
System.out.println("Welcome to the AP Computer Science calculator!!");
System.out.println();
System.out.println("Please use the following format in your expressions: (double)(space)(+,-,*,/...)(space)(double)");
System.out.println("or: (symbol)(space)(double)");
System.out.println();
String input = MethodToReadInput();
while (input != null)//exit the loop and the program when input is null
{
MethodtoEvaluateInput(input);//process the input
input = MethodToReadInput();//ask the user for the next input
}
}
public static String MethodToReadInput()
{
Scanner kb = null;
try
{
kb = new Scanner(System.in);
System.out.print("Enter an expression, or quit to exit: ");
String expression = kb.nextLine();
if (expression.equalsIgnoreCase("quit"))
{
System.out.println("Goodbye!");
return null;
}
else
{
return expression;
}
}
finally
{//always close the Scanner before leaving the method
if (kb != null)
kb.close();
}
}
此外，您应该遵循Java Naming Convention并为您的方法使用较短的名称。
答案 1 :(得分：0)
这样做：
public static String MethodToReadInput() {
Scanner kb = new Scanner(System.in);
System.out.print("Enter an expression, or quit to exit: ");
String expression = kb.nextLine();
if (expression.equalsIgnoreCase("quit")) {
System.out.println("Goodbye!");
return "";
}
else {
return expression;
}
通过返回一个空字符串，您知道在用户想要退出时要查找的内容。它必须是您返回的空字符串，因为您的方法应该返回一个字符串。还需要添加这个return语句，因为编译器会抱怨，因为它可能会到达非void函数的末尾（返回某些东西），而不会实际到达return语句（所以当你输入if语句时）它现在）。如果指定返回类型，则必须为所有可能性指定返回大小写。换句话说，你必须总是回复你所说的话。
答案 2 :(得分：0)
尝试简化你的代码，并使用do-while-loop代替while循环应该产生更好的代码，同时至少做一个循环，然后在进行下一个循环之前检查下一个条件，但同时将检查条件首先，如果可以，它将进行循环。所以这是代码：
public class Calculator {
public static void main(String[] args) throws IOException {
System.out.println("Welcome to the AP Computer Science calculator!!");
System.out.println();
System.out.println("Please use the following format in your expressions: (double)(space)(+,-,*,/...)(space)(double)");
System.out.println("or: (symbol)(space)(double)");
System.out.println();
String expression = "";
do {
Scanner kb = new Scanner(System.in);
System.out.print("Enter an expression, or quit to exit: ");
expression = kb.nextLine();
if (expression.equalsIgnoreCase("quit"))
System.out.println("Goodbye!");
else
MethodtoEvaluateInput(expression);
} while (!expression.equalsIgnoreCase("quit"));
inRn.close();
inSw.close();
}
}
答案 3 :(得分：0)
有几件事情需要解决。
首先，让我们回答您的实际问题。你可以有很多选择。
while ( ! expression.equals("quit") )。while ( expression != null )，这比字符串比较更有效。但您的程序存在其他设计问题：
您一次又一次地调用相同的方法来检索相同的内容。那些方法一次又一次地拆分字符串 - 一个相对繁重的操作。您应该只有一个parseExpression()方法返回您的标记，然后测试这些标记是否代表一元运算符或二元运算符。有点像：
String [] tokens = parseExpression( expression );
if ( isUnaryExpression( tokens ) ) {
String operator = tokens[0];
String operand = tokens[1];
// Do something with operator and operand.
} else if ( isBinaryExpression( tokens ) ) {
String operator = tokens[1];
String operand1 = tokens[0];
String operand2 = tokens[2];
// Do something with operator and operands {
} else {
System.err.println( "Bad expression!" );
}
您正在从主电话中拨打MethodToReadInput两次。这意味着它将读取一个输入，不执行任何操作，然后读取另一个将传递给MethodToTestInput的输入。放弃第一个电话，这是不必要的。
main方法实际上甚至不应该调用MethodToReadInput。调用该方法应该成为MethodToTestInput的责任。因此，您只需从MethodToTestInput()调用main，而无需传递任何参数。所以结构应该是：
"quit"。在循环内部，调用表达式处理程序方法。parseExpression()方法，检查令牌是什么，做数学运算。最后，关于您的命名问题：
您没有为方法MethodThatDoesThis命名。您应该将其命名为doThis。这使得阅读代码更容易，因为它实际上描述了正在发生的事情。所以我将这些方法命名为：
getNextExpression runCalculator或doCalculatorMainLoop或类似的东西。parseAndCalculate。或者沿着这些方向发展。