Difference between StringBuilder and StringBuffer

Question

What is the main difference between StringBuffer and StringBuilder? Is there any performance issues when deciding on any one of these?

Answer 1

Check the internals of synchronized append method of StringBuffer and non-synchronized append method of StringBuilder.

StringBuffer:

public StringBuffer(String str) {
    super(str.length() + 16);
    append(str);
}

public synchronized StringBuffer append(Object obj) {
    super.append(String.valueOf(obj));
    return this;
}

public synchronized StringBuffer append(String str) {
    super.append(str);
    return this;
}

StringBuilder:

public StringBuilder(String str) {
    super(str.length() + 16);
    append(str);
}

public StringBuilder append(Object obj) {
    return append(String.valueOf(obj));
}

public StringBuilder append(String str) {
    super.append(str);
    return this;
}

Since append is synchronized, StringBuffer has performance overhead compared to StrinbBuilder in multi-threading scenario. As long as you are not sharing buffer among multiple threads, use StringBuilder, which is fast due to absence of synchronized in append methods.