数组索引超出界限 – Java
我已经开始研究我的第一个Java程序，这是一个简单的计算器，但是我得到一个错误声称我的数组已经超出界限。 我试图调试它以查看其中的原因和原因，以及遵循纸上的代码，这两个代码都显示了我期望和希望的结果。 因此，我看不出问题究竟在哪里。 代码不完整。
根据调试器，错误发生在这一行：
answer = outputNum.get(operationIndex) * outputNum.get(operationIndex+1); 这是我目前拥有的代码的主要部分：
private class ButtonHandler implements ActionListener { /* * "outputNum" stores the numbers entered in order. * "orderOfOperations" stores all numbers in order after multiplication and division has been taken care of. * "operationList" stores the mathematical operations entered in order. * "currentNum" stores the most recently inputed numbers. * "currentString" stores the most recently inputed string of numbers. * "answer" stores temporary values and ultimately the answer to the inputed equation. * "start" stores whether or not the equals button has been pressed and a new equation has started. */ ArrayList outputNum = new ArrayList (0); ArrayList orderOfOperations = new ArrayList (0); ArrayList operationList = new ArrayList (0); Double currentNum = 0.0; String currentString = "0"; Double answer = 0.0; boolean start = false; public void actionPerformed(ActionEvent event) { if(event.getSource() == equalsBtn) { /* Takes the current numbers string and convert it into a double. * Let the order of operations be the inputed order for now. * "operationIndex" to get values inside of the unchanging arrays "outputNum" and "operationList". * "orderIndex" to get values inside of the changing array "orderOfOperations". */ currentNum = Double.parseDouble(currentString); outputNum.add(currentNum); orderOfOperations = outputNum; int operationIndex = 0; int orderIndex = 0; //Cycle through the mathematical operations that occur in the current equation. for(String operation : operationList) { if(operation == "x" || operation == "÷") { // Multiply/divide numbers with the multiply/divide operations together. if(operation == "x") { answer = outputNum.get(operationIndex) * outputNum.get(operationIndex+1); } else { answer = outputNum.get(operationIndex) / outputNum.get(operationIndex+1); } // Replace numbers multiplied/divided in the above statement with the new answer. orderOfOperations.remove(orderIndex); orderOfOperations.set(orderIndex, answer); orderIndex++; } operationIndex++; } // Reset variables to the default values for the new equation. System.out.println(orderOfOperations); outputString = answer.toString(); answer = 0.0; currentNum = 0.0; currentString = "0"; outputNum.clear(); operationList.clear(); orderOfOperations.clear(); start = true; } else if(event.getSource() == additionBtn || event.getSource() == subtractionBtn || event.getSource() == multiplicationBtn || event.getSource() == divisionBtn) { // Sets the text fields text blank if this is the start of a new equation. if(start) { outputString = ""; start = false; } /* * Takes the current numbers string and convert it into a double. * Add the mathematical operation and reset the current number. */ currentNum = Double.parseDouble(currentString); outputNum.add(currentNum); operationList.add(event.getActionCommand()); currentString = "0"; outputString = String.format("%s%s", outputString, event.getActionCommand()); } else { // Sets the text fields text blank if this is the start of a new equation. if(start) { outputString = ""; start = false; } // Adds the button value to the text field text and the current number being inputed. currentString = String.format("%s%s", currentString, event.getActionCommand()); outputString = String.format("%s%s", outputString, event.getActionCommand()); } outputScreen.setText(outputString); } }
这是我得到的错误消息：
Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException: Index: 2, Size: 2 at java.util.ArrayList.RangeCheck(ArrayList.java:547) at java.util.ArrayList.get(ArrayList.java:322) at MainWindow$ButtonHandler.actionPerformed(MainWindow.java:141) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236) at java.awt.Component.processMouseEvent(Component.java:6414) at javax.swing.JComponent.processMouseEvent(JComponent.java:3275) at java.awt.Component.processEvent(Component.java:6179) at java.awt.Container.processEvent(Container.java:2084) at java.awt.Component.dispatchEventImpl(Component.java:4776) at java.awt.Container.dispatchEventImpl(Container.java:2142) at java.awt.Component.dispatchEvent(Component.java:4604) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4618) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4279) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4209) at java.awt.Container.dispatchEventImpl(Container.java:2128) at java.awt.Window.dispatchEventImpl(Window.java:2492) at java.awt.Component.dispatchEvent(Component.java:4604) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:717) at java.awt.EventQueue.access$400(EventQueue.java:82) at java.awt.EventQueue$2.run(EventQueue.java:676) at java.awt.EventQueue$2.run(EventQueue.java:674) at java.security.AccessController.doPrivileged(Native Method) at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:86) at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:97) at java.awt.EventQueue$3.run(EventQueue.java:690) at java.awt.EventQueue$3.run(EventQueue.java:688) at java.security.AccessController.doPrivileged(Native Method) at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:86) at java.awt.EventQueue.dispatchEvent(EventQueue.java:687) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188) at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
当operationIndex等于outputNum的最后一个元素索引时，则operationIndex + 1将大于最后一个元素索引：因此您的exception
你最好使用从索引1开始的for循环，然后执行：
// assuming that operationList and outputNum always // have the same number of elements for (int i = 1; i < operationList.size(); i++) { ... answer = outputNum.get(i - 1) * outputNum.get(i); ... }
或者，使用您当前的循环，但执行：
// operationIndex++; // remove this and use .. if (++operationIndex >= outputNum.size()) break;
您只需在列表中添加一个项目：
currentNum = Double.parseDouble(currentString); outputNum.add(currentNum);
然后你尝试访问似乎是索引operationindex +1的第二个对象，它不存在：
answer = outputNum.get(operationIndex) * outputNum.get(operationIndex+1);