Java:printf 堆栈错误

Question

我试图将 println 转换为 printf，这就是我得到的结果。

//*********************************Output File*********************************
//Create a file with the information entered 
//and the information processed
 public void outputFile() throws IOException{
String payFileOutput=null;
PrintWriter file= new PrintWriter("DataOutput.txt");
file.printf("Your total expenses per month are %10f\n", 
   format.format(getTotalCost()));
file.printf("Your college tuition is %10f\n", format.format(getTuition()));
file.printf("Your rent is %10f\n", format.format(getRent()));
  if(pay==1)
   payFileOutput="Savings";
  else if(pay==2)
   payFileOutput="Loans";
  else if(pay==3)
   payFileOutput="Freelance Work";
  else
   ;
  file.printf("Your payment method is %10f\n", payFileOutput);
  file.printf("Your amount entered for the payment method is %10f\n", 
     format.format(getPayment()));
  if(totalCost<0){
   file.printf("You still need: %5f per month\n", 
     format.format(getTotalCost()));}
  else{
   file.printf("\nYour budget seems good");}
  file.close();
 }
}  

---

Exception in thread "AWT-EventQueue-0" java.util.IllegalFormatConversionException: f != java.lang.String
 at java.util.Formatter$FormatSpecifier.failConversion(Formatter.java:4011)
 at java.util.Formatter$FormatSpecifier.printFloat(Formatter.java:2738)
 at java.util.Formatter$FormatSpecifier.print(Formatter.java:2683)
 at java.util.Formatter.format(Formatter.java:2449)
 at java.io.PrintWriter.format(PrintWriter.java:878)
 at java.io.PrintWriter.printf(PrintWriter.java:777)
 at FinanceRev1.outputFile(FinanceRev1.java:173)
 at FinanceGUI$button2Listener.actionPerformed(FinanceGUI.java:286)
 at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2012)
 at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2335)
 at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:404)
 at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
 at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:253)
 at java.awt.Component.processMouseEvent(Component.java:6175)
 at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
 at java.awt.Component.processEvent(Component.java:5940)
 at java.awt.Container.processEvent(Container.java:2105)
 at java.awt.Component.dispatchEventImpl(Component.java:4536)
 at java.awt.Container.dispatchEventImpl(Container.java:2163)
 at java.awt.Component.dispatchEvent(Component.java:4362)
 at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4461)
 at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4125)
 at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4055)
 at java.awt.Container.dispatchEventImpl(Container.java:2149)
 at java.awt.Window.dispatchEventImpl(Window.java:2478)
 at java.awt.Component.dispatchEvent(Component.java:4362)
 at java.awt.EventQueue.dispatchEvent(EventQueue.java:604)
 at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
 at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
 at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
 at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:185)
 at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:177)
 at java.awt.EventDispatchThread.run(EventDispatchThread.java:138)

---

更新:解决方案:数字格式将指示的数字格式化为字符串，并且因为我有 %f( float )，所以很明显我会得到一个堆栈，因为您不能将字符串引用到一个花车。感谢 MIrC 上的 HydroKirby。

Answer 1

在

file.printf("Your payment method is %10f\n", payFileOutput);

payFileOutput 的类型是 String，而 %10f 格式说明符期望使用 float ，因此您的提示错误:

java.util.IllegalFormatConversionException: f != java.lang.String

该特定行会导致此错误，但如果该方法的返回类型也是字符串，您对 format() 的调用也可能产生类似的不匹配。