InstantiationException thrown for my Class Extension

I have written the following class, there rest of the code within the class is @Overrides, please let me know if the rest of the code is relevant here and I shall add it.

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

Which when my tests are run I get thrown InstantiationException's.

Looking at the API I have tried to go through what throws this error and narrow it down but to no avail, here are the logs for one of the errors.

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)

I am running this test

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);
}
}

And then these tests fail

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);
}
``
</details>
# 答案1
**得分**: 2
来自 [`InstantiationException`][1] 的 Java 文档：
&gt; 当应用程序尝试使用 `Class` 类中的 `newInstance` 方法创建类的实例时，如果指定的类对象无法实例化，则会抛出此异常。实例化可能因各种原因而失败，包括但不限于：
&gt;
&gt;  - 类对象表示一个**抽象类**、一个接口、一个数组类、一个基本类型或 void
&gt;  - 类没有无参数构造函数
你的 `ListCmdTest` 类是抽象的，所以 jUnit 无法实例化它。
[1]: https://docs.oracle.com/javase/8/docs/api/java/lang/InstantiationException.html
<details>
<summary>英文:</summary>
From javadoc of [`InstantiationException`][1]:
&gt; Thrown when an application tries to create an instance of a class using the `newInstance` method in class `Class`, but the specified class object cannot be instantiated. The instantiation can fail for a variety of reasons including but not limited to:
&gt;
&gt;  - the class object represents an **abstract class**, an interface, an array class, a primitive type, or void
&gt;  - the class has no nullary constructor
Your `ListCmdTest` class is `abstract`, so jUnit cannot instantiate it.
[1]: https://docs.oracle.com/javase/8/docs/api/java/lang/InstantiationException.html
</details>