Error: Non-static method append(char) cannot be referenced from a static context

[paul]

I'm having trouble trying to use StringBuffer() on the following code. The error I'm getting is:
ChangeBase.java:91: non-static method append(char) cannot be referenced from a static context.

public void actionPerformed(ActionEvent e)
{
//....
    for(int j = 0; j<count; j++){ 
        test = ChangeBase.pop();
        System.out.println(test);
        StringBuffer.append(str.charAt(test));//where str is just a string. This is line 91.
     }
 }
StringBuffer buf = new StringBuffer();
jtfResult.setText(buf.toString());
 //...

Anyone has an idea what the error is refering to? Thanks

[coco]

You need to create an instance of the StringBuffer, as you are here:

StringBuffer buf = new StringBuffer();

Greetings.