Bug 4240 Can't edit class path entry (1GKEPIF)
There is no way to edit an existing entry for a library on the Java Build Path project properties page (other than editing the .classpath file directly). NOTES: EG (9/22/2001 11:42:11 AM) this is particularly annoying for variables. we should have an Edit button when a variable is selected.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/SourceContainerWorkbookPage.java
Control control= fFoldersList.getListControl(composite);
		GridData gd= new GridData(GridData.FILL_BOTH);
		gd.horizontalIndent= converter.convertWidthInCharsToPixels(2);
		gd.widthHint= converter.convertWidthInCharsToPixels(50);
		gd.heightHint= converter.convertWidthInCharsToPixels(15);
		gd.grabExcessHorizontalSpace= true;
		control.setLayoutData(gd);
		
		control= fFoldersList.getButtonBox(composite);
		gd= new GridData(gd.VERTICAL_ALIGN_FILL + gd.HORIZONTAL_ALIGN_FILL);
		control.setLayoutData(gd);
		
		int buttonBarWidth= converter.convertWidthInCharsToPixels(24);
		fFoldersList.setButtonsMinWidth(buttonBarWidth);
	
		fSWTControl= composite;
		
		return composite;
	}
	
	private Shell getShell() {
		if (fSWTControl != null) {
			return fSWTControl.getShell();
		}
		return JavaPlugin.getActiveWorkbenchShell();
	}
	
	
	private class SourceContainerAdapter implements IListAdapter, IDialogFieldListener {