JDeveloper is a lightweight (JFC) application. As such, using heavyweight (AWT) controls directly in the Java Visual Editor will not work as expected. Heavyweight components always obscure lightweight components, including the lightweight JDeveloper environment (including the Code Editor and UML Modelers).
The Java Visual Editor includes a proxy mechanism for registering lightweight proxies to represent heavyweight controls for instantiation in the Java Visual Editor. By default JDeveloper includes lightweight proxies for all the standard AWT controls.
Registering a Java Visual Editor Proxy for Custom Components
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