idea中输入的代码，软件表示无法识别，求解决方案

想在JComboBox中加入元素，如下图，发现无法识别addItem；
idea预设版本与所用JDK版本一致

    JComboBox c1=new JComboBox();
    c1.addItem("suit one");
    c1.addItem("suit two");

附addItem JDK13.0.2:

addItem

public void addItem​(E item)

Adds an item to the item list. This method works only if the JComboBox uses a mutable data model.
Warning: Focus and keyboard navigation problems may arise if you add duplicate String objects. A workaround is to add new objects instead of String objects and make sure that the toString() method is defined. For example:

comboBox.addItem(makeObj("Item 1"));

comboBox.addItem(makeObj("Item 1"));

...

private Object makeObj(final String item) {
return new Object() { public String toString() { return item; } };
}

Parameters:

item - the item to add to the list

intellij idea的Java无法识别addItem是因为什么