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

Better use StringBuilder since it is not synchronized and therefor better performance. StringBuilder is a drop-in replacement of the older StringBuffer.

Answer 2

StringBuffer:

• Multi-Thread
• Synchronized
• Slow than StringBuilder

StringBuilder

• Single-Thread
• Not-Synchronized
• Faster than ever String

Answer 3

StringBuffer is synchronized, but StringBuilder is not. As a result, StringBuilder is faster than StringBuffer.

Answer 4

Since StringBuffer is synchronized, it needs some extra effort, hence based on perforamance, its a bit slow than StringBuilder.

Answer 5

String is an immutable object which means the value cannot be changed where as StringBuffer is mutable.

The StringBuffer is Synchronized hence thread safe where as StringBuilder is not and suitable for only single threaded instances.

Answer 6

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.