将字符串解析为double / integer时如何解决NumberFormatException

Question

I've written a program & I've built a GUI for it. When I try to run it, it throws an exception NumberFormatException and here's all I got :

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String
    at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
    at sun.misc.FloatingDecimal.parseDouble(Unknown Source)
    at java.lang.Double.parseDouble(Unknown Source)
    at newtp.GUI$2.actionPerformed(GUI.java:219)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$400(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

So what do I have to do to solve my problem?

Answer 1

Your problem is that your string is empty

java.lang.NumberFormatException: empty String at 

To solve this problem, you should fill the string with a string representation of a number (eg 3 for a string or 7.7 for a double)

Would be best if you show us your code to see where the problem is.

Example:

Ff you do the following

String string1 = "";
int int1 = Integer.parseInt(string1);

you will receive the exception you received since Java is not able to find the matching int value for and empty string.

If you do

String string2 = "3";
int int2 = Integer.parseInt(string2);

you won't receive an exception, but a variable called int2 containing the value 3.

Answer 2

One solution, as Phiwa said, is just not to pass in an empty string. It's probably better to handle the issue, though.

You can use something like this to assign a default value if the entered value isn't of the correct type:

int x;
try {
    //whatever you're doing to parse the string...probably x = Integer.parseInt("32"); or something
catch(NumberFormatException e) {
    e.printStackTrace();
    x = 12; //or whatever default value you want
}

Answer 3

我已经在变量为空时将其强制转换为变量，该变量在actionListener中，所以我带来了值（使用textField.getText（）;），解析完成了……我忘了引入所有方法了。为帮助大家:)））