Eclipse插件开发报错：SampleView类型层次结构不一致求助

我正在学习《创建Eclipse插件》教程，目前卡在创建视图的环节：

最后一步是为org.eclipse.ui.views扩展点编写“Hello World!”视图的Java类，结果出现错误提示："The hierarchy of the type SampleView is inconsistent."（类型SampleView的继承层次不一致）

查资料了解到，这个错误通常是因为继承类（此处为ViewPart）的jar包未加入项目构建路径。但我的目标平台已经包含org.eclipse.ui.views插件（该插件应该包含org.eclipse.ui.views.jar）：

希望能得到解决思路！

更新：附上相关文件内容 #

plugin.xml #

<?xml version="1.0" encoding="UTF-8"?>
<?eclipse version="3.4"?>
<plugin>

   <extension
         point="org.eclipse.ui.commands">
      <category
            id="com.example.helloworld.commands.category"
            name="Sample Category">
      </category>
      <command
            categoryId="com.example.helloworld.commands.category"
            name="Display Hello World"
            id="com.example.helloworld.commands.sampleCommand">
      </command>
   </extension>
   <extension
         point="org.eclipse.ui.handlers">
      <handler
            class="com.example.helloworld.handlers.SampleHandler"
            commandId="com.example.helloworld.commands.sampleCommand">
      </handler>
   </extension>
   <extension
         point="org.eclipse.ui.bindings">
      <key
            commandId="com.example.helloworld.commands.sampleCommand"
            schemeId="org.eclipse.ui.defaultAcceleratorConfiguration"
            contextId="org.eclipse.ui.contexts.window"
            sequence="M1+6">
      </key>
   </extension>
   <extension
         point="org.eclipse.ui.menus">
      <menuContribution
            locationURI="menu:org.eclipse.ui.main.menu?after=additions">
         <menu
               id="com.example.helloworld.menus.sampleMenu"
               label="Sample Menu"
               mnemonic="M">
            <command
                  commandId="com.example.helloworld.commands.sampleCommand"
                  id="com.example.helloworld.menus.sampleCommand"
                  mnemonic="S">
            </command>
         </menu>
      </menuContribution>
      <menuContribution
            locationURI="toolbar:org.eclipse.ui.main.toolbar?after=additions">
         <toolbar
               id="com.example.helloworld.toolbars.sampleToolbar">
            <command
                  id="com.example.helloworld.toolbars.sampleCommand"
                  commandId="com.example.helloworld.commands.sampleCommand"
                  icon="icons/sample.png"
                  tooltip="Say hello world">
            </command>
         </toolbar>
      </menuContribution>
   </extension>
   <extension
         point="org.eclipse.ui.views">
      <category
            id="com.example.helloworld.view.helloworldcategory"
            name="Hello World!">
      </category>
      <view
            category="com.example.helloworld.view.helloworldcategory"
            class="com.example.helloworld.view.SampleView"
            id="com.example.helloworld.view.helloworldview"
            name="Hello World!"
            restorable="true">
      </view>
   </extension>

</plugin>

MANIFEST.MF #

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Helloworld
Bundle-SymbolicName: com.example.helloworld;singleton:=true
Bundle-Version: 1.0.0.qualifier
Bundle-Vendor: EXAMPLE
Require-Bundle: org.eclipse.ui
Automatic-Module-Name: com.example.helloworld
Bundle-RequiredExecutionEnvironment: JavaSE-17

内容的提问来源于stack exchange，提问作者Piscercube