为我的类扩展引发了InstantiationException

Question

我已经编写了以下类，该类中的其余代码是@Overrides，请告诉我其余代码是否与此处相关，我将添加它。

public class ListCmd extends LibraryCommand {
public ListCmd(String argumentInput) {
super(CommandType.LIST, argumentInput);
}
...

当我的测试运行时，我会抛出InstantiationException。

看看API，我试图了解是什么导致了这个错误，并将其缩小，但没有成功，下面是其中一个错误的日志。

java.lang.InstantiationException
at java.base/jdk.internal.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:48)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
at org.junit.runners.BlockJUnit4ClassRunner.createTest(BlockJUnit4ClassRunner.java:217)
at org.junit.runners.BlockJUnit4ClassRunner$1.runReflectiveCall(BlockJUnit4ClassRunner.java:266)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.BlockJUnit4ClassRunner.methodBlock(BlockJUnit4ClassRunner.java:263)
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$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)

我正在运行此测试

import org.junit.Before;
import java.util.ArrayList;
import java.util.List;
public abstract class ListCmdTest extends CommandTest {
protected static final String SHORT_ARGUMENT = "short";
protected static final String LONG_ARGUMENT = "long";
@Override
protected CommandType getCmdType() {
return CommandType.LIST;
}
@Before
public void setup() {
testCommand = new ListCmd(SHORT_ARGUMENT);
testLibrary = new LibraryData();
List<BookEntry> bookData = new ArrayList<>();
bookData.add(new BookEntry("TitleA", new String[]{"AuthorA"}, 3.2f, "ISBNA", 500));
bookData.add(new BookEntry("TitleB", new String[]{"AuthorB"}, 4.3f, "ISBNB", 400));
bookData.add(new BookEntry("TitleC", new String[]{"AuthorC"}, 1.3f, "ISBNC", 300));
FieldTestUtils.setPrivateField(testLibrary, testLibrary.getClass(), "books", bookData);
}
}

然后这些测试没有通过

import org.junit.Test;
import static org.junit.Assert.assertEquals;
public abstract class CommandTest {
protected static final String TITLE_ARGUMENT = "TITLE";
protected static final String AUTHOR_ARGUMENT = "AUTHOR";
protected static final String BLANK_ARGUMENT = "";
protected LibraryCommand testCommand;
protected LibraryData testLibrary;
public CommandTest() {
testCommand = null;
testLibrary = null;
}
protected abstract CommandType getCmdType();
// ------------------------- initialisation tests --------------------
@Test
public void testClassCommandExtension() {
assertEquals(testCommand.getClass() + " has unexpected superclass.", LibraryCommand.class,
testCommand.getClass().getSuperclass());
}
@Test
public void testCtorSuperclassCall() {
CommandTestUtils.checkCtorSuperclassCall(testCommand, getCmdType());
}
// ------------------------- parseArguments tests --------------------
@Test
public void testIsParseArgumentsOverridden() {
CommandTestUtils.checkIfParseArgumentsIsOverridden(testCommand);
}
// ------------------------- execute tests --------------------
@Test(expected = NullPointerException.class)
public void testExecuteLibraryDataNull() {
testCommand.execute(null);
}
``

Answer 1

来自InstantiationException:的javadoc

当应用程序尝试使用类Class中的newInstance方法创建类的实例，但无法实例化指定的类对象时抛出。实例化可能由于多种原因而失败，包括但不限于：

• 类对象表示抽象类、接口、数组类、基元类型或void
• 该类没有null构造函数

您的ListCmdTest类是abstract，因此jUnit无法实例化它。