两种方法的区别，是返回值得关系吗？

public class Test {
public static void stringReplace(String text){

text= text + "c";
}
public static void bufferReplace(StringBuffer text){
text = text.append("c");
}
public static void main(String args[]){
String textString = new String("java");
StringBuffer textBuffer = new StringBuffer("java");
stringReplace(textString);
bufferReplace(textBuffer);
System.out.println(textString + " " + textBuffer);
}


}