Guava map storing class instance as key and int value

Question

I am trying to use Guava's collections to create a map that will store a class instance as the key and an Integer number as the value. So something like this:

Key - Value

FooOne - 1
FooTwo - 2
FooThree - 3
FooFour - 4

I have this in the code right now:

private ClassToInstanceMap<Object> classRanking = MutableClassToInstanceMap.create();
classRanking.put(FooOne.class, 0);
classRanking.put(FooTwo.class, 1);
classRanking.put(FooThree.class, 2);
classRanking.put(FooFour.class, 3);

But that throws an error when run:

java.lang.ClassCastException: Cannot cast java.lang.Integer to com.jer.abc.test.FooOne
    at java.lang.Class.cast(Unknown Source)
    at com.google.common.collect.MutableClassToInstanceMap.cast(MutableClassToInstanceMap.java:82)
    at com.google.common.collect.MutableClassToInstanceMap.access$000(MutableClassToInstanceMap.java:36)
    at com.google.common.collect.MutableClassToInstanceMap$1.checkKeyValue(MutableClassToInstanceMap.java:67)
    at com.google.common.collect.MutableClassToInstanceMap$1.checkKeyValue(MutableClassToInstanceMap.java:64)
    at com.google.common.collect.MapConstraints$ConstrainedMap.put(MapConstraints.java:313)
    at com.fmr.gps.web.support.PortfolioInsightsSupport.populateRankingMap(PortfolioInsightsSupport.java:33)
    at com.fmr.gps.web.support.PortfolioInsightsSupport.<init>(PortfolioInsightsSupport.java:29)
    at com.fmr.gps.web.PortfolioInsightsSupportTest.setUp(PortfolioInsightsSupportTest.java:38)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

So I was thinking about using a plain old java map but this thread tells me to do otherwise. So any ideas on how to fix this?

Answer 1

ClassToInstanceMap is for when you want to do stuff like classRanking.put(FooOne.class, new FooOne()) , ie the values will be instances of the key. But 0 is not an instance of FooOne , it's just an Integer . You just want a normal Map<Class<?>, Integer> , so use a HashMap or something.