common methods between String and String buffer [duplicate]

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Possible Duplicate:

String, StringBuffer, and StringBuilder

What 开发者_Python百科are common methods between String and StringBuffer? And what is the difference between string and string buffer?

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The biggest difference is that String is immutable and StringBuffer is mutable.

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StringBuffer lets you join strings faster. For example the following code:

String s = "Initial string ";
for (int i = 0; i < 100; i++) {
    s = s + i;
}

on every iteration creates a string representing integer i and than also creates a new string of s and i joined together and moves s reference to this new object. It does not reuse the same s object by expanding its content.

StringBuffer lets you append string more efficiently. There is also a newer version of this class called StringBuilder which is basically StringBuffer without synchronization.

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The first few lines on the StringBuffer JavaDoc give a pretty good answer:

A thread-safe, mutable sequence of characters. A string buffer is like a String, but can be modified.

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The most obvious shared methods are those specified by the interface implemented by both String and StringBuffer (as well as StringBuilder): Appendable. It provides 3 methods for appending other values.

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When you need to concatenate many String literal together, then it might be better off for you to use a StringBuffer object, and as when you are done with the concatenation, turning it into a String object using the toString() method.

EDIT: Please ignore the lines below

The below instantiates 6 String objects in the String pool theoretically.

String a = "A" + "B" + "C" + "D" + "E";