#java exception

Do you catch NullPointerException or have you swallowed Exceptions by simply catching them and doing nothing. Have you wondered whether to throw an Exception or to catch it before it reaches the parent method. As a general rule,  catching any RuntimeException is almost always a code smell. Probably, you could look after your code or…

Summary

Java® Exception and abrupt exit on Mac OS X version 10.10 Yosemite

Description

When running MATLAB on Mac OS X version 10.10 Yosemite, the following Java exception is reported:

java.lang.NullPointerException at com.mathworks.widgets.WindowsWidgetFactory $SearchAndClearButton.anyText(WindowsWidgetFactory.java:187) at com.mathworks.widgets.WindowsWidgetFactory $SearchAndClearButton.getIcon(WindowsWidgetFactory.java:195) at com.apple.laf.AquaButtonUI.setThemeBorder(AquaButtonUI.java:113) at com.apple.laf.AquaButtonUI.installDefaults(AquaButtonUI.java:80) at javax.swing.plaf.basic.BasicButtonUI.installUI(BasicButtonUI.java:88) at javax.swing.JComponent.setUI(JComponent.java:664) at javax.swing.AbstractButton.setUI(AbstractButton.java:1807) at javax.swing.JButton.updateUI(JButton.java:146) at javax.swing.AbstractButton.init(AbstractButton.java:2172) at javax.swing.JButton.<init>(JButton.java:136) . . .

Following this, MATLAB may exit abruptly.

What is null in java

What is Null in Java what is Null in java

nullpointerexception

What is Null Object ?

When you create an object and not initializing it with any reference the object remain null.it means nothing . Null is not a valid object instance, so there is no memory allocated for it. It is simply a value that indicates that the object reference is not currently referring to an object.

What cause…

When you are working on large scale Java application, you will encounter one or many exceptions like below. This blog summarizes what I have experienced so far and may not cover all scenarios.

  java.lang.NoSuchMethodException

The exception happens when you are trying to invoke a method that is not present in target class. The exception is prominent if your application is using reflection API. If reflection was not used, then it could be that partial build was deployed. You had compiled your Java class with a bunch of dependent classes but at some point in time dependent classes were modified (methods removed or changed) and deployed independently.

java.lang.reflect.InvocationTargetException

It happens when you are directly or indirectly using reflection in your application. This exception is more visible if you are using Axis or any Web Services where bean marshalling and unmarshalling happen via reflection API. The exception can be tricky to resolve because the original exception is wrapped in InvocationTargetException. You probably want to get handle of target exception by calling getTargetException() on InvocationTargetException object and analyze it.

java.lang.IllegalAccessException

Again it happens when you are using reflection in your application at runtime. Your code is trying to access method or member variable that are out of reach (e.g. private, protected) and should not be allowed to access. I think this class should be part of reflect package along with InvocationTargetException.

java.lang.ClassNotFoundException

This one can be really easy or extremely tricky to figure out. The classloader cannot find the class it is looking for. You need to first check the obvious places like your classpath and jar files where your class supposed to reside. Check your reflection code as well.

The trickiness comes if you are in J2EE environment with multiple classloaders. For example you have parent-first classloader setting in your appserver configuration. Your EAR file has class A which is referenced by class B in parent classloader, then class A cannot be found and ClassNotFoundException will be thrown. So in this case, even if you have class A present in your classpath, it cannot be found by classloader.

java.lang.NoClassDefFoundError

Technically this is an error not an exception. At runtime, the class you are trying to load is not found or class definition is not correct (similar to linkage error in C/C++). It could be you have given invalid class name or the class itself is not there. You should check your classpath settings. It could also be triggered by ClassNotFoundException meaning if Test.java was using Test2.java and once compiled if you remove Test2.class at runtime, then Test.class would complain the following

Exception in thread "main" java.lang.NoClassDefFoundError:     Test2 at Test.main(Test.java:7)     Caused by: java.lang.ClassNotFoundException: Test2     at java.net.URLClassLoader$1.run(URLClassLoader.java:202)