NPE in StdDateFormat hashCode and equals

[kazuki43zoo]

Occur NullPointerException in hashCode() and equals(Object) method.
Please implements these methods correctly.

Thanks.

Test Cases

@Test
public void testHashCode() {
    StdDateFormat.instance.hashCode();
}

@Test
public void testEquals() {
    StdDateFormat.instance.equals(new StdDateFormat());
}

Stack Traces

java.lang.NullPointerException
    at java.text.DateFormat.hashCode(DateFormat.java:739)
        ...
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

java.lang.NullPointerException
    at java.text.DateFormat.equals(DateFormat.java:751)
        ...
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

[cowtowncoder]

I would like to see more of stack trace to know why these methods are invoked.

[kazuki43zoo]

It is a small sample for repro. For example, NPE is occurred when add the StdDateFormat instance into HashSet.

public class FooTest {
    @Test
    public void testHashCode() {
        Set<DateFormat> set = new HashSet<>();
        set.add(StdDateFormat.instance);
    }
}

• Full stak trace

java.lang.NullPointerException
    at java.text.DateFormat.hashCode(DateFormat.java:739)
    at java.util.HashMap.hash(HashMap.java:338)
    at java.util.HashMap.put(HashMap.java:611)
    at java.util.HashSet.add(HashSet.java:219)
    at com.github.kazuki43zoo.sample.FooTest.testHashCode(FooTest.java:20)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:117)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:234)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:74)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

I tried same operation using the SimpleDateFormat.

@Test
public void testHashCode2() {
    Set<DateFormat> set = new HashSet<>();
    set.add(new SimpleDateFormat("yyyyMMdd"));
}

This code is no problem.

[cowtowncoder]

Ok, went ahead and added minimal code to avoid NPE.

[kazuki43zoo]

Thanks for fix !!