Ejemplo

public class ClassA {
private final StringBuffer stringObject = new StringBuffer("A new String");
private StringBuffer nonConstantString = new StringBuffer("Changing String");

public void method(){
StringBuffer localString;
final StringBuffer localConstantString;
}
}

Solución
Declare objetos de constante (final) StringBuffer utilizando String en su lugar.

public class ClassA {
private final String stringObject = "A new String";
private StringBuffer nonConstantString = new StringBuffer("Changing String");

public void method(){
StringBuffer localString;
final String localConstantString;
}
}