Java's String,stringbuffer,stringbuilder class

In the Java language, the classes used to handle strings are commonly used in 3: string, StringBuffer, StringBuilder.

Their similarities and differences:

1) are final classes, are not allowed to be inherited;

2) String length is immutable, stringbuffer, StringBuilder length is variable;

3) StringBuffer is thread-safe and StringBuilder is not thread-safe. This means that many of the methods in the StringBuffer class use the Synchronized keyword modifier, which allows multithreading to manipulate strings.

Three classes most of the time performance: StringBuilder "StringBuffer" String.

4) The use of StringBuffer and StringBuilder methods is basically the same

Test the performance using the following code:

1  Public classTeststringclass {2 3     Private Final intLOOPS = 200000;4     Private FinalString constant_string = "Java-string";5 6      Public Static voidMain (string[] args) {7 8         NewTeststringclass (). teststring ();9         NewTeststringclass (). Teststringbuffer ();Ten         NewTeststringclass (). Teststringbullder (); One     } A  -      Public voidteststring () { -String string = ""; the         LongCurrentTime =System.currenttimemillis (); -          for(inti = 0; i < LOOPS; i++) { -string + =constant_string; -         } +         LongEndTime =System.currenttimemillis (); -System.out.println ("String:" + (EndTime-currenttime)); +     } A  at      Public voidTeststringbuffer () { -StringBuffer StringBuffer =NewStringBuffer (); -         LongCurrentTime =System.currenttimemillis (); -          for(inti = 0; i < LOOPS; i++) { - stringbuffer.append (constant_string); -         } in         LongEndTime =System.currenttimemillis (); -System.out.println ("StringBuffer:" + (EndTime-currenttime)); to     } +  -      Public voidTeststringbullder () { theStringBuilder StringBuilder =NewStringBuilder (); *         LongCurrentTime =System.currenttimemillis (); $          for(inti = 0; i < LOOPS; i++) {Panax Notoginseng stringbuilder.append (constant_string); -         } the         LongEndTime =System.currenttimemillis (); +System.out.println ("Stringbullder:" + (EndTime-currenttime)); A     } the}

Results:

string:149549
Stringbuffer:9
Stringbullder:7

The difference is obvious. String has a bad performance.

However, if you use string constants in the compile phase, the performance of string will be very fast.

Summarize:

1. Using string constants at compile time, use string. For example: String haha = "I" + "AM" + "Java";

2. Without regard to thread safety, the append efficiency of the StringBuilder object is higher than the StringBuffer object's append efficiency higher than the "+" connection operation of the string object.

3. In the case of multi-threaded synchronization, it is recommended to use StringBuffer.

Java's String,stringbuffer,stringbuilder class