Swing UI Thread exception

What I am doing is that, when I get the params from user, I am initializing those params using constructuors on my class. and running a thread on my class. When I debug I am getting the below exception. I guess it is not stopping for the entire process to execute. I am new to GWT, can anybody let me know how can I do that.

Code

Thread thread = new Thread(new ExportData(param 1, param 2));

thread.start();

I have run method which will be executed based on the params.

Exception

java.lang.RuntimeException: Error running on Swing UI thread

at com.google.gwt.dev.SwingUI.invokeAndWait(SwingUI.java:401)

at com.google.gwt.dev.SwingUI.initialize(SwingUI.java:245)

at com.google.gwt.dev.DevModeBase.doStartup(DevModeBase.java:889)

at com.google.gwt.dev.DevMode.doStartup(DevMode.java:424)

at com.google.gwt.junit.JUnitShell.doStartup(JUnitShell.java:932)

at com.google.gwt.dev.DevModeBase.startUp(DevModeBase.java:1058)

at com.google.gwt.junit.JUnitShell.getUnitTestShell(JUnitShell.java:708)

at com.google.gwt.junit.JUnitShell.runTest(JUnitShell.java:653)

at com.google.gwt.junit.client.GWTTestCase.runTest(GWTTestCase.java:441)

at junit.framework.TestCase.runBare(TestCase.java:134)

at junit.framework.TestResult$1.protect(TestResult.java:110)

at junit.framework.TestResult.runProtected(TestResult.java:128)

at junit.framework.TestResult.run(TestResult.java:113)

at junit.framework.TestCase.run(TestCase.java:124)

at com.google.gwt.junit.client.GWTTestCase.run(GWTTestCase.java:296)

at junit.framework.TestSuite.runTest(TestSuite.java:232)

at junit.framework.TestSuite.run(TestSuite.java:227)

at junit.framework.TestSuite.runTest(TestSuite.java:232)

at junit.framework.TestSuite.run(TestSuite.java:227)

at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:83)

at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49)

at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)

at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)

at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)

at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)

at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Caused by: java.lang.reflect.InvocationTargetException

at java.awt.EventQueue.invokeAndWait(EventQueue.java:1055)

at com.google.gwt.dev.SwingUI.invokeAndWait(SwingUI.java:397)

... 25 more

Caused by: java.lang.NullPointerException

at com.google.gwt.dev.SwingUI.loadImageIcon(SwingUI.java:142)

at com.google.gwt.dev.SwingUI.loadImageIcon(SwingUI.java:124)

at com.google.gwt.dev.SwingUI$3.run(SwingUI.java:247)

at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:199)

at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:646)

at java.awt.EventQueue.access$000(EventQueue.java:84)

at java.awt.EventQueue$1.run(EventQueue.java:607)

at java.awt.EventQueue$1.run(EventQueue.java:605)

at java.security.AccessController.doPrivileged(Native Method)

at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)

at java.awt.EventQueue.dispatchEvent(EventQueue.java:616)

at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)

at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)

at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

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