Exemplo

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

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

Solução

Declare objetos constantes (final) StringBuffer utilizando String.

public class ClassA {
private final String stringObject = "Um novo String";
private StringBuffer nonConstantString = new StringBuffer("Alterando String");

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