Efficient version number comparison in Java

We all know that the client or device side related to the version number of the place will inevitably involve the version upgrade problem, this time we need to compare the size of the version number, String type version number is how to compare it? Traditionally we will use CompareTo or string to double the comparison, so there will be a bug, today I would like to talk about two ways of comparison: split according to "." To split, and then compare the size of each split out of the string, the following code: (in addition, I use the version number does not contain letters, so do not consider the case contains letters, this can make corresponding changes)

public static int Compare (String v1,string v2) {string [] xx=v1.split ("\ \"); String [] yy=v2.split ("\ \"); int A=0;try {for (int x=0,y=0;x<xx.length| | y<yy.length;x++,y++) {int left= (x<xx.length)? Integer.parseint (Xx[x]): 0;int right= (y<yy.length)? Integer.parseint (Yy[y]): 0;if (left>right) {a=1;} else if (left==right) {continue;} Else{a=-1;} a=0;}} catch (Exception e) {//Todo:handle exception}return A;}

But from a performance point of view, this approach is not the most perfect, we have a similar to the bottom of the way, you can better save performance, running speed has improved, nonsense said, look at the code:

        public static  Int compare2 (string v1,string v2) {int i=0,j=0,x=0,y=0;int v1len=v1.length ();int  V2len=v2.length (); Char c;do {while (I<v1len) {//calculates the number C=v1.charat before the point in V1 (i++); if (c>= ' 0 '   && c<= ' 9 ') {x=x*10+ (c ' 0 ');//c-' 0 ' represents the ASCLL difference between the two}else if (c== '. ') {break;//End}else{//Invalid character}}while (J<v2len) {//Calculates the number V2 (j + +) before the point in C=v2.charat; if (c>= ' 0 '  &&  c<= ' 9 ') {y=y*10+ (c ' 0 ');} Else if (c== '. ') {break;//End}else{//Invalid character}}if (x<y) {return -1;} Else if (x>y) {return 1;} Else{x=0;y=0;continue;}}  while  ((i<v1len)  | |   (J<v2len)); return 0;} 

public static void Main (string[] args) {System.out.println ("Compare performance start >>>>>>>>>>>> > "); String v1= "0.10.20.1"; String v2= "0.001.02.3"; Long Starttime=system.currenttimemillis (); for (int i=0;i<1000000;i++) {Compare (V1, v2);} Long Endtime=system.currenttimemillis (); SYSTEM.OUT.PRINTLN ("split mode comparison 1 million times" + (Endtime-starttime)); Long Starttime1=system.currenttimemillis (); for (int i=0;i<1000000;i++) {compare2 (v1, v2);} Long Endtime1=system.currenttimemillis (); System.out.println ("character char method compares 1 million times" + (ENDTIME1-STARTTIME1));}

The results of the test are as follows:

Compare performance Start >>>>>>>>>>>>>

Split mode comparison 1 million times 538

Character Char mode comparison 1 million times 28

As a result, the first time to write a blog, the wrong place also please correct

This article is from the "Java into God's Road" blog, please be sure to keep this source http://yao012.blog.51cto.com/12765256/1915026

Efficient version number comparison in Java