Bug 52064 Content assist in "New Class" Dialog shows interfaces
Content Assist is available for the superclass in M7. However it also lists interfaces. If an interface is selected, the generated class "extends" it instead of "implementing" it.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/wizards/NewTypeWizardPage.java
/**
	 * Sets the enclosing type. The method updates the underlying model 
	 * and the text of the control.
	 * 
	 * @param type the enclosing type
	 * @param canBeModified if <code>true</code> the enclosing type field is
	 * editable; otherwise it is read-only.
	 */	
	public void setEnclosingType(IType type, boolean canBeModified) {
		fCurrEnclosingType= type;
		fCanModifyEnclosingType= canBeModified;
		String str= (type == null) ? "" : JavaModelUtil.getFullyQualifiedName(type); 
		fEnclosingTypeDialogField.setText(str);
		updateEnableState();
	}
	
	/**
	 * Returns the selection state of the enclosing type checkbox.
	 * 
	 * @return the selection state of the enclosing type checkbox
	 */
	public boolean isEnclosingTypeSelected() {
		return fEnclosingTypeSelection.isSelected();
	}
	/**
	 * Sets the enclosing type checkbox's selection state.
	 * 
	 * @param isSelected the checkbox's selection state
	 * @param canBeModified if <code>true</code> the enclosing type checkbox is
	 * modifiable; otherwise it is read-only.