Java 构造函数定义处的NullPointerException
我正在尝试测试以下类:Java 构造函数定义处的NullPointerException,java,oop,powermock,powermockito,Java,Oop,Powermock,Powermockito,我正在尝试测试以下类: public final class ClassA { private final ClassB member; public ClassA() { this.member = new ClassB(); } } 以下是测试类别: @RunWith(PowerMockRunner.class) @PrepareForTest({ClassA.class, ClassB.class}) public final class ClassATest
public final class ClassA {
private final ClassB member;
public ClassA() {
this.member = new ClassB();
}
}
以下是测试类别:
@RunWith(PowerMockRunner.class)
@PrepareForTest({ClassA.class, ClassB.class})
public final class ClassATest {
@Mock
private ClassB mocked;
private ClassA testClass;
@Before
public void initTest() {
PowerMockito.whenNew(ClassB.class).withNoArguments().thenReturn(mocked);
testClass = new ClassA();
}
现在,问题是我得到了一个nullpointerexception,它的stacktrace如下所示:
java.lang.NullPointerException
[junit] at a.a.i.ClassA.<init>(ClassA.java:44)
[junit] at a.a.i.ClassATest.init(ClassATest.java:53)
[junit] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[junit] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
[junit] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[junit] at java.lang.reflect.Method.invoke(Method.java:606)
[junit] at org.junit.internal.runners.MethodRoadie.runBefores(MethodRoadie.java:132)
[junit] at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:95)
[junit] at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:294)
[junit] at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:127)
[junit] at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTest(PowerMockJUnit47RunnerDelegateImpl.java:82)
[junit] at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:282)
[junit] at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:86)
[junit] at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
[junit] at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:207)
[junit] at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:146)
[junit] at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:120)
[junit] at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:33)
[junit] at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:45)
[junit] at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:122)
[junit] at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:106)
[junit] at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:53)
[junit] at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:59)
[junit] at junit.framework.JUnit4TestAdapter.run(JUnit4TestAdapter.java:38)
[junit] at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.run(JUnitTestRunner.java:532)
[junit] at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.launch(JUnitTestRunner.java:1165)
[junit] at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.main(JUnitTestRunner.java:988)
java.lang.NullPointerException
[junit]在a.a.i.ClassA.(ClassA.java:44)
[junit]位于a.a.i.ClassATest.init(ClassATest.java:53)
[junit]位于sun.reflect.NativeMethodAccessorImpl.invoke0(本机方法)
[junit]位于sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
[junit]位于sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[junit]位于java.lang.reflect.Method.invoke(Method.java:606)
[junit]位于org.junit.internal.runners.MethodRoadie.runBefores(MethodRoadie.java:132)
[junit]位于org.junit.internal.runners.MethodRoadie.runBeforesthenTestTheAfter(MethodRoadie.java:95)
[junit]位于org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:294)
[junit]位于org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:127)
[junit]位于org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTest(PowerMockJUnit47RunnerDelegateImpl.java:82)
[junit]位于org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runbeforesthenTestthenAfter(PowerMockJUnit44RunnerDelegateImpl.java:282)
[junit]位于org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:86)
[junit]位于org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
[junit]位于org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:207)
[junit]位于org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:146)
[junit]位于org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:120)
[junit]位于org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:33)
[junit]位于org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:45)
[junit]位于org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:122)
[junit]位于org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:106)
[junit]位于org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:53)
[junit]位于org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:59)
[junit]位于junit.framework.JUnit4TestAdapter.run(JUnit4TestAdapter.java:38)
[junit]位于org.apache.tools.ant.taskdefs.optional.junit.junitestrunner.run(junitestrunner.java:532)
[junit]位于org.apache.tools.ant.taskdefs.optional.junit.junitestrunner.launch(junitestrunner.java:1165)
[junit]位于org.apache.tools.ant.taskdefs.optional.junit.junitestrunner.main(junitestrunner.java:988)
ClassA的第44行是
公共甲级(){
ClassATest的第52行是
testClass=newclassa()
我以前从未在构造函数定义中遇到过NullPointerException,因此我不知道该如何处理它。任何帮助都将不胜感激。我想当您将成员声明为final时,u应该立即实例化它
在去构造器之前试着这样做,看看会发生什么我知道这个问题是关于NPE的,但是你应该重新考虑你的测试策略,而不是解决这个问题。为什么
如果ClassA负责ClassB实例的创建和使用,而您决定不注入ClassB对象,那么为什么要尝试模拟它?您的测试不应该依赖于实现细节,因此,如果您不在任何地方注入ClassB,您就不应该模拟它。这种方法根本不推荐。对象不应该被响应不允许创建自己的依赖项。它们应该在其构造函数中提供(或通过setter方法提供) 我建议您像这样更改构造函数
public final class ClassA {
private final ClassB member;
public ClassA(ClassB member) {
this.member = member;
}
}
如果您想保留代码,您可以添加一个用于测试的构造函数(尽管也不建议仅为测试目的添加代码)
什么是ClassB构造函数?ClassB的定义是什么?ClassB有默认构造函数(未显式重写),我将使用完整堆栈跟踪更新。不,没有额外的初始化块。您猜错了。
final
实例字段可以在构造函数中设置。(一般来说,猜测不是有用的答案*
public final class ClassA {
private final ClassB member;
public ClassA() {
this(new ClassB());
}
// Default visibility so it's only visible in its package
// Added for testing purposes
ClassA(ClassB member) {
this.member = member;
}
}