Question

使用下面的Java测试代码会发生一些奇怪的事情。这是用Spring编写的。

ResourceType resourceType1 = new ResourceType(RESOURCE_TYPE_NAME);
resourceType1 = resourceTypeService.addResourceType(resourceType1);

ResourceType resourceType2 = new ResourceType(RESOURCE_TYPE_NAME_2);
resourceType2 = resourceTypeService.addResourceType(resourceType2);

List<ResourceType> all = resourceTypeService.getAll();
List<ResourceType> myObjects = new ArrayList<>();
for (ResourceType resourceType : all) {
    if(resourceType.getId() == resourceType1.getId()
            || resourceType.getId() == resourceType2.getId()){
        myObjects.add(resourceType);
    }
}

assertTrue(myObjects.get(0).getId() == resourceType1.getId());

运行时，它会在IndexOutOfBounds来电时返回.get(0)。

这很奇怪，因为resourceType1和resourceType2在all列表中有ID。

这是调试代码的结果：

插入后的资源类型1：

resourceType1 = {ResourceType@5986} 
 id = 179

插入后的资源类型1：

resourceType2 = {ResourceType@5987} 
 id = 180

全部在getAll()

之后

all = {ArrayList@5988}  size = 37
 ..........
 35 = {ResourceType@5986} 
  id = 179
 36 = {ResourceType@5987} 
  id = 180

这是调试数据。

为什么不满足if条件？

更新＃1

错误堆栈跟踪：

java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    at java.util.ArrayList.rangeCheck(ArrayList.java:653)
    at java.util.ArrayList.get(ArrayList.java:429)
    at com.test.ihbs.service.ResourceTypeServiceTest.test_getAll(xxx.java:107)
    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.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:73)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:82)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:73)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:224)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:83)
    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$2.evaluate(ParentRunner.java:268)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:68)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:163)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.runTestClass(JUnitTestClassExecuter.java:86)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.execute(JUnitTestClassExecuter.java:49)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassProcessor.processTestClass(JUnitTestClassProcessor.java:64)
    at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:50)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
    at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.messaging.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:32)
    at org.gradle.messaging.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:93)
    at com.sun.proxy.$Proxy2.processTestClass(Unknown Source)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.processTestClass(TestWorker.java:106)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
    at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.messaging.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:360)
    at org.gradle.internal.concurrent.DefaultExecutorFactory$StoppableExecutorImpl$1.run(DefaultExecutorFactory.java:64)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

Answer 1

As I said in comments you can't compare Long using == comparator. It only works for values between (-128, 127) and only if they are not created using new keyword. It works because those values are cached by JVM so comparing reference return true.

Look here or here.

1)

Integer i = 100;
Integer p = 100;
if (i == p)  System.out.println("i and p are the same.");
if(i.equals(p))  System.out.println("i and p contain the same value.");

The output is:

i and p are the same.
i and p contain the same value.

2)

Integer i = 200;
Integer p = 200;
if (i == p)  System.out.println("i and p are the same.");
if(i.equals(p))  System.out.println("i and p contain the same value.");

The output is:

i and p contain the same value.

3)

Integer i = new Integer (100);
Integer p = new Integer(100);
if(i==p) System.out.println(“i and p are the same object”);
if(i.equals(p)) System.out.println(“ i and p contain the same value”);

In this circumstance, the output is only:

i and p contain the same value

Answer 2

“==”始终比较值的内存位置或对象引用。 equals方法总是比较values.but equals也间接使用“==”运算符来比较值。整数使用整数缓存来存储-128到+ 127之间的值。如果==运算符用于检查-128到127之间的任何值，则返回true。除了这些值之外，它返回false。

Refer the link 了解更多信息。

如果条件未正确评估

2 个答案: