The difference between replace and ReplaceAll in Java

Replace and replaceall are commonly used substitution characters in Java, and their differences are:

1) The Replace parameter isCharAndcharsequence, which can support the substitution of characters, also support the substitution of strings (charsequence is the meaning of string sequences, in other words, the string);
2) The parameters of the ReplaceAll areRegex, which is the substitution of regular expressions, for example, by ReplaceAll ("\\d", "*") to convert all numeric characters of a string to asterisks;

The same point is all replace, that is, a character or string in the source string is all replaced by the specified character or string, if you want to replace only the first occurrence, you can use Replacefirst (), this method is based on the substitution of regular expressions, but unlike replaceall (), Replaces only the first occurrence of the string;
In addition, if the parameter data used by ReplaceAll () and Replacefirst () are not based on regular expressions, the effect of replacing the string with replace () is the same, that is, the operation of the string is also supported;
Also note: The contents of the source string have not changed since the substitution operation was performed.

Examples are as follows:

string src = new string ("ab43a2c43d");

System.out.println (Src.replace ("3", "F")); =>ab4f2c4fd.
System.out.println (Src.replace (' 3 ', ' f ')); =>ab4f2c4fd.
System.out.println (Src.replaceall ("\\d", "F")); =>abffafcffd.
System.out.println (Src.replaceall ("A", "F")); =>fb43fc23d.
System.out.println (Src.replacefirst ("\\d," F ")); =>abf32c43d
System.out.println (Src.replacefirst ("4", "H")); =>abh32c43d.


How to replace "\" in a string with "\ \":

String Msgin;
String msgout;
Msgout=msgin.replaceall ("\\\\", "\\\\\\\\");
Reason:
' \ ' is an escape character in Java, so it takes two to represent one. For example, System.out.println ("\ \"); only one "\" is printed. But ' \ ' is also an escape character in a regular expression (ReplaceAll's argument is a regular expression) and requires two to represent one. So: \\\\ is converted to \\,\\ by Java and converted to \ by the regular expression.
Same
CODE: \\\\\\\\
Java: \\\\
Regex: \ \


There are several ways to replace '/' in a string with ' \ ':

msgout= Msgin.replaceall ("/", "\\\\");
msgout= msgin.replace ("/", "\ \");
msgout= msgin.replace ('/', ' \ \ ');

The difference between replace and ReplaceAll in Java (RPM)