无法从静态上下文引用非静态字符串
当试图从另一个类调用一个方法我的方法作为错误
private class equalsButton implements ActionListener { // makes the equals button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("="); InfixToPostfixParens.convert(operator); // Line with error } } 不能从静态上下文中引用非静态字符串。 变量不是静态的，但我仍然有任何想法的问题吗？
现在我的主要程序的批量（对不起在地方的草率编码）
/** * Graphics of the calculator * * @author Collin Blake * @version (2-28-11) */ import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.*; import java.awt.*; import java.awt.event.*; public class SimpleCalculator extends JFrame { JTextField textField; String operator = ""; public SimpleCalculator() { setTitle("Simple Calculator"); // makes the window for the calculator setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setLayout(new GridLayout(0, 1)); JPanel topPanel = new JPanel(); // Initilaized for the text window topPanel.setLayout(new GridLayout()); textField = new JTextField(10); textField.addActionListener(new NumEntered()); topPanel.add(textField); add(topPanel); JPanel centerPanel = new JPanel(); // center panel initilaized centerPanel.setLayout(new GridLayout(0, 4)); JButton oneButton = new JButton("1"); // initilaized values for each // button in their menus JButton twoButton = new JButton("2"); JButton threeButton = new JButton("3"); JButton plusButton = new JButton("+"); JButton fourButton = new JButton("4"); JButton fiveButton = new JButton("5"); JButton sixButton = new JButton("6"); JButton minusButton = new JButton("-"); JButton sevenButton = new JButton("7"); JButton eightButton = new JButton("8"); JButton nineButton = new JButton("9"); JButton timesButton = new JButton("*"); JButton zeroButton = new JButton("0"); JButton decimalButton = new JButton("."); JButton powerButton = new JButton("^"); JButton divideButton = new JButton("/"); JButton LParButton = new JButton("("); JButton RParButton = new JButton(")"); JButton equalsButton = new JButton("="); // creates equals button JButton allClearButton = new JButton("AC"); oneButton.addActionListener(new oneButton()); // initilaized values for // each button's // actionlistener twoButton.addActionListener(new twoButton()); threeButton.addActionListener(new threeButton()); plusButton.addActionListener(new plusButton()); fourButton.addActionListener(new fourButton()); fiveButton.addActionListener(new fiveButton()); sixButton.addActionListener(new sixButton()); minusButton.addActionListener(new minusButton()); sevenButton.addActionListener(new sevenButton()); eightButton.addActionListener(new eightButton()); nineButton.addActionListener(new nineButton()); timesButton.addActionListener(new timesButton()); zeroButton.addActionListener(new zeroButton()); decimalButton.addActionListener(new decimalButton()); powerButton.addActionListener(new powerButton()); divideButton.addActionListener(new divideButton()); LParButton.addActionListener(new LParButton()); RParButton.addActionListener(new RParButton()); equalsButton.addActionListener(new equalsButton()); // creates action // listener for // equals allClearButton.addActionListener(new allClearButton()); centerPanel.add(oneButton); // Adds the buttons to the sub panel centerPanel.add(twoButton); centerPanel.add(threeButton); centerPanel.add(plusButton); centerPanel.add(fourButton); centerPanel.add(fiveButton); centerPanel.add(sixButton); centerPanel.add(minusButton); centerPanel.add(sevenButton); centerPanel.add(eightButton); centerPanel.add(nineButton); centerPanel.add(timesButton); centerPanel.add(zeroButton); centerPanel.add(decimalButton); centerPanel.add(powerButton); centerPanel.add(divideButton); centerPanel.add(LParButton); centerPanel.add(RParButton); centerPanel.add(equalsButton); centerPanel.add(allClearButton); add(centerPanel); // Creates the panel with buttons pack(); setLocationRelativeTo(null); } private class NumEntered implements ActionListener { @Override public void actionPerformed(ActionEvent e) { // do nothing } } private class oneButton implements ActionListener { // makes the one button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("1"); operator += "1"; textField.setText(operator); } } private class twoButton implements ActionListener { // makes the two button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("2"); operator += "2"; textField.setText(operator); } } private class threeButton implements ActionListener { // makes the three button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("3"); operator += "3"; textField.setText(operator); } } private class fourButton implements ActionListener { // makes the four button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("4"); operator += "4"; textField.setText(operator); } } private class fiveButton implements ActionListener { // makes the five button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("5"); operator += "5"; textField.setText(operator); } } private class sixButton implements ActionListener { // makes the six button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("6"); operator += "6"; textField.setText(operator); } } private class sevenButton implements ActionListener { // makes the seven button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("7"); operator += "7"; textField.setText(operator); } } private class eightButton implements ActionListener { // makes the eight button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("8"); operator += "8"; textField.setText(operator); } } private class nineButton implements ActionListener { // makes the nine button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("9"); operator += "9"; textField.setText(operator); } } private class zeroButton implements ActionListener { // makes the zerobutton listener @Override public void actionPerformed(ActionEvent e) { System.out.println("0"); operator += "0"; textField.setText(operator); } } private class plusButton implements ActionListener { // makes the plus button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("+"); operator += "+"; textField.setText(operator); } } private class minusButton implements ActionListener { // makes the minus button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("-"); operator += "-"; textField.setText(operator); } } private class timesButton implements ActionListener { // makes the times button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("*"); operator += "*"; textField.setText(operator); } } private class divideButton implements ActionListener { // makes the divide button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("/"); operator += "/"; textField.setText(operator); } } private class allClearButton implements ActionListener { // makes the all clear button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("AC"); operator = ""; textField.setText(operator); } } private class decimalButton implements ActionListener { // makes the decimal button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("."); operator += "."; textField.setText(operator); } } private class equalsButton implements ActionListener { // makes the equals button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("="); InfixToPostfixParens.convert(operator); } } private class LParButton implements ActionListener { // makes the ( button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("("); operator += "("; textField.setText(operator); } } private class RParButton implements ActionListener { // makes the ) button listener @Override public void actionPerformed(ActionEvent e) { System.out.println(")"); operator += ")"; textField.setText(operator); } } private class powerButton implements ActionListener { // makes the ^ button listener @Override public void actionPerformed(ActionEvent e) { System.out.println("^"); operator += "^"; textField.setText(operator); } } }
InfixToPostfixParens的代码
import java.util.Stack; import java.util.EmptyStackException; import java.util.regex.Pattern; import java.util.Scanner; /** * Translates an infix expression with parentheses to a postfix expression. * * @author Koffman & Wolfgang */ public class InfixToPostfixParens { // Nested Class /** Class to report a syntax error. */ public static class SyntaxErrorException extends Exception { /** * Construct a SyntaxErrorException with the specified message. * * @param message * The message */ SyntaxErrorException(String message) { super(message); } } // Data Fields /** The operator stack */ private Stack operatorStack; /** The operators */ private static final String OPERATORS = "-+*/()"; /** * The Pattern to extract tokens A token is either a string of digits (\d+) * or a JavaIdentifier or an operator */ private static final Pattern pattern = Pattern.compile("\\d+\\.\\d*|\\d+|" + "\\p{javaJavaIdentifierStart}\\p{javaJavaIdentifierPart}*" + "|[" + OPERATORS + "]"); /** The precedence of the operators, matches order of OPERATORS. */ private static final int[] PRECEDENCE = { 1, 1, 2, 2, -1, -1 }; /** The postfix string */ private StringBuilder postfix; /** * Convert a string from infix to postfix. * * @param infix * The infix expression * @throws SyntaxErrorException */ public String convert(String infix) throws SyntaxErrorException { operatorStack = new Stack(); postfix = new StringBuilder(); Scanner scan = new Scanner(infix); try { // Process each token in the infix string. String nextToken; while ((nextToken = scan.findInLine(pattern)) != null) { char firstChar = nextToken.charAt(0); // Is it an operand? if (Character.isJavaIdentifierStart(firstChar) || Character.isDigit(firstChar)) { postfix.append(nextToken); postfix.append(' '); } // Is it an operator? else if (isOperator(firstChar)) { processOperator(firstChar); } else { throw new SyntaxErrorException( "Unexpected Character Encountered: " + firstChar); } } // End while. // Pop any remaining operators // and append them to postfix. while (!operatorStack.empty()) { char op = operatorStack.pop(); // Any '(' on the stack is not matched. if (op == '(') { throw new SyntaxErrorException( "Unmatched opening parenthesis"); } postfix.append(op); postfix.append(' '); } // assert: Stack is empty, return result. return postfix.toString(); } catch (EmptyStackException ex) { throw new SyntaxErrorException("Syntax Error: The stack is empty"); } } /** * Method to process operators. * * @param op * The operator * @throws EmptyStackException */ private void processOperator(char op) { if (operatorStack.empty() || op == '(') { operatorStack.push(op); } else { // Peek the operator stack and // let topOp be the top operator. char topOp = operatorStack.peek(); if (precedence(op) > precedence(topOp)) { operatorStack.push(op); } else { // Pop all stacked operators with equal // or higher precedence than op. while (!operatorStack.empty() && precedence(op) // top of stack operator precedence. if (op != ')') { operatorStack.push(op); } } } } /** * Determine whether a character is an operator. * * @param ch * The character to be tested * @return true if ch is an operator */ private boolean isOperator(char ch) { return OPERATORS.indexOf(ch) != -1; } /** * Determine the precedence of an operator. * * @param op * The operator * @return the precedence */ private int precedence(char op) { return PRECEDENCE[OPERATORS.indexOf(op)]; } }
您的代码与以下（编译）有何不同？
import java.awt.event.ActionEvent; import java.awt.event.ActionListener; public class Example1 { private String operator; private class equalsButton implements ActionListener { public void actionPerformed(ActionEvent e) { System.out.println("="); InfixToPostfixParens.convert(operator); } } } public class InfixToPostfixParens { public static void convert(String s) { // Do something useful } }