Clearing a string buffer builder after loop

Question

How do you clear the string buffer in Java after a loop so the next iteration uses a clear string buffer

User · Answer

Already good answer there  Just add a benchmark result for StringBuffer and StringBuild performance difference use new instance in loop or use setLength 0  in loop   The summary is  In a large loop   StringBuilder is much faster than StringBuffer  Create new StringBuilder instance in loop have no difference with setLength 0    setLength 0  have very very very tiny advantage than create new instance   StringBuffer is slower than StringBuilder by create new instance in loop setLength 0  of StringBuffer is extremely slower than create new instance in loop    Very simple benchmark  I just manually changed the code and do different test     public class StringBuilderSpeed   public static final char ch     new char    a   b   c   d   e   f   g   h   i     public static void main String a         int loopTime   99999999      long startTime   System currentTimeMillis        StringBuilder sb   new StringBuilder        for int i   0   i  lt  loopTime  i             for char c   ch               sb append c                     sb setLength 0             long endTime   System currentTimeMillis        System out println  Time cost       endTime - startTime           New StringBuilder instance in loop      Time cost  3693  3862  3624  3742  StringBuilder setLength      Time cost  3465  3421  3557  3408  New StringBuffer instance in loop      Time cost  8327  8324  8284  StringBuffer setLength     Time cost  22878  23017  22894  Again StringBuilder setLength to ensure not my labtop got some issue to use such long for StringBuffer setLength  -  Time cost  3448

User · Answer

You have two options     Either use     sb setLength 0       It will just discard the previous data  which will be garbage collected later      Or use     sb delete 0  sb length         A bit slower as it is used to delete sub sequence      NOTE    Avoid declaring StringBuffer or StringBuilder objects within the loop else it will create new objects with each iteration  Creating of objects requires system resources  space and also takes time  So for long run  avoid declaring them within a loop if possible

User · Answer

public void clear StringBuilder s        s setLength 0       Usage   StringBuilder v   new StringBuilder    clear v     for readability  I think this is the best solution

User · Answer

The easiest way to reuse the StringBuffer is to use the method setLength    public void setLength int newLength   You may have the case like  StringBuffer sb   new StringBuffer  HelloWorld       after many iterations and manipulations sb setLength 0      reuse sb

User · Answer

StringBuffer sb   new SringBuffer       do something wiht it sb   new StringBuffer      i think this code is faster

User · Answer

buf delete 0   buf length

User · Answer

One option is to use the delete method as follows   StringBuffer sb   new StringBuffer    for  int n   0  n  lt  10  n         sb append  a           This will clear the buffer    sb delete 0  sb length         Another option  bit cleaner  uses setLength int len    sb setLength 0     See Javadoc for more info

User · Answer

I suggest creating a new StringBuffer  or even better  StringBuilder  for each iteration  The performance difference is really negligible  but your code will be shorter and simpler

[java] Clearing a string buffer/builder after loop

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