We Keep Coding

Java replace strings between two commas

String = "9,3,5,*****,1,2,3"
I'd like to simply access "5", which is between two commas, and right before "*****"; then only replace this "5" to other value.
How could I do this in Java?

You can try using the following regex replacement:
String input = "9,3,5,*****,1,2,3";
input = input.replaceAll("[^,]*,\\*{5}", "X,*****");
Here is an explanation of the regex:
[^,]*, match any number of non-comma characters, followed by one comma
\\*{5} followed by five asterisks
This means to match whatever CSV term plus a comma comes before the five asterisks in your string. We then replace this with what you want, along with the five stars in the original pattern.
Demo here:
Rextester

I'd use a regular expression with a lookahead, to find a string of digits that precedes ",*****", and replace it with the new value. The regular expression you're looking for would be \d+(?=,\*{5}) - that is, one or more digits, with a lookahead consisting of a comma and five asterisks. So you'd write
newString = oldString.replaceAll("\\d+(?=,\\*{5})", "replacement");
Here is an explanation of the regex pattern used in the replacement:
\\d+ match any numbers of digits, but only when
(?=,\\*{5}) we can lookahead and assert that what follows immediately
is a single comma followed by five asterisks
It is important to note that the lookahead (?=,\\*{5}) asserts but does not consume. Hence, we can ignore it with regards to the replacement.

I considered newstr be "6"
String str = "9,3,5,*****,1,2,3";
char newstr = '6';
str = str.replace(str.charAt(str.indexOf(",*") - 1), newstr);
Also if you are not sure about str length check for IndexOutOfBoundException
and handle it

You could split on , and then join with a , (after replacing 5 with the desired value - say X). Like,
String[] arr = "9,3,5,*****,1,2,3".split(",");
arr[2] = "X";
System.out.println(String.join(",", arr));
Which outputs
9,3,X,*****,1,2,3

you can use spit() for replacing a string
String str = "9,3,5,*****,1,2,3";
String[] myStrings = str.split(",");
String str1 = myStrings[2];

Validate string a+b

I would like to validate if the particular string is true or not in form of a + b
If input = a + b true
If input = a + false
if input = + b false
where a and b can be any string characters

I can think of a couple of ways:
Use a regex to match a "+" the characters before and after it.
Use String.indexOf("+") to find a "+" character and test the value of the index to see if it as the start or end of the string.
(Don't forget the cases where a or b could contain a "+" character; i.e. multiple "+" characters in the string.)

You can use regular expression (regex) to test the string. In java you can use the Pattern and Matcher classes to test if a string matches a given regex. The regex you want to use is:
String regex = ".* \\+ .*";
This regex will test for a string in the following form: "[characters] + [characters]".
Here is more information about the regex in java.

How to replace all numbers in java string

I have string like this String s="ram123",d="ram varma656887"
I want string like ram and ram varma so how to seperate string from combined string
I am trying using regex but it is not working
PersonName.setText(cursor.getString(cursor.getColumnIndex(cursor
.getColumnName(1))).replaceAll("[^0-9]+"));

The correct RegEx for selecting all numbers would be just [0-9], you can skip the +, since you use replaceAll.
However, your usage of replaceAll is wrong, it's defined as follows: replaceAll(String regex, String replacement). The correct code in your example would be: replaceAll("[0-9]", "").

You can use the following regex: \d for representing numbers. In the regex that you use, you have a ^ which will check for any characters other than the charset 0-9
String s="ram123";
System.out.println(s);
/* You don't need the + because you are using the replaceAll method */
s = s.replaceAll("\\d", ""); // or you can also use [0-9]
System.out.println(s);

To remove the numbers, following code will do the trick.
stringname.replaceAll("[0-9]","");

Please do as follows
String name = "ram varma656887";
name = name.replaceAll("[0-9]","");
System.out.println(name);//ram varma
alternatively you can do as
String name = "ram varma656887";
name = name.replaceAll("\\d","");
System.out.println(name);//ram varma
also something like given will work for you
String given = "ram varma656887";
String[] arr = given.split("\\d");
String data = new String();
for(String x : arr){
data = data+x;
}
System.out.println(data);//ram varma

i think you missed the second argument of replace all. You need to put a empty string as argument 2 instead of actually leaving it empty.
try
replaceAll(<your regexp>,"")

you can use Java - String replaceAll() Method.
This method replaces each substring of this string that matches the given regular expression with the given replacement.
Here is the syntax of this method:
public String replaceAll(String regex, String replacement)
Here is the detail of parameters:
regex -- the regular expression to which this string is to be matched.
replacement -- the string which would replace found expression.
Return Value:
This method returns the resulting String.
for your question use this
String s = "ram123", d = "ram varma656887";
System.out.println("s" + s.replaceAll("[0-9]", ""));
System.out.println("d" + d.replaceAll("[0-9]", ""));

Change a specific letter / space from a string into another one

Isn't it possible to Change a specific digit/letter or even a space in a string and set it to another one?
Example:
String test = "name1 name2 name3 name4"
and I want to convert it into another String so that it could look like this:
String test2 = "name1+name2+name3+name4"
So how can I tell it to set all "spaces" to a +?

Use replaceAll()
test2=test.replaceAll("\\s","+");

Try String.replaceAll()
test2 = test.replaceAll("\\s","+");
Note :
(Regex) \s : (Description) A whitespace character, short for [ \t\n\x0b\r\f]
and since this is a special character it is preceeded by one more \

Use String#replaceAll("\\s", "+") method

You should look into repalceAll() in String class
test2=test1.replaceAll(" ","+");

What you'll need to do is search the string for the spaces and each time you've found one replace it with a designated character.
In Java there are functions to do this for you. Such as ReplaceAll(oldStr, newStr), where oldStr can accept a regular expression and newStr is the replacement.
String test = "name1 name2 name3 name4";
test = test.ReplaceAll(" ","+");
System.out.println(test);
The output is:
name1+name2+name3+name4
Instead of typing a space: " "
You may add the exact character code (ASCII code) you wish to replace by using:
Character.toString ((char) i)
Where i is the ASCII number.
So the equivalent would be:
test = test.ReplaceAll(Character.toString ((char) 32), Character.toString ((char) 43));
Hope this helps :)

Difference between String replace() and replaceAll()

What's the difference between java.lang.String 's replace() and replaceAll() methods,
other than later uses regex? For simple substitutions like, replace . with / ,
is there any difference?

In java.lang.String, the replace method either takes a pair of char's or a pair of CharSequence's (of which String is a subclass, so it'll happily take a pair of String's). The replace method will replace all occurrences of a char or CharSequence. On the other hand, the first String arguments of replaceFirst and replaceAll are regular expressions (regex). Using the wrong function can lead to subtle bugs.

Q: What's the difference between the java.lang.String methods replace() and replaceAll(), other than that the latter uses regex.
A: Just the regex. They both replace all :)
http://docs.oracle.com/javase/8/docs/api/java/lang/String.html
PS:
There's also a replaceFirst() (which takes a regex)

Both replace() and replaceAll() replace all occurrences in the String.
Examples
I always find examples helpful to understand the differences.
replace()
Use replace() if you just want to replace some char with another char or some String with another String (actually CharSequence).
Example 1
Replace all occurrences of the character x with o.
String myString = "__x___x___x_x____xx_";
char oldChar = 'x';
char newChar = 'o';
String newString = myString.replace(oldChar, newChar);
// __o___o___o_o____oo_
Example 2
Replace all occurrences of the string fish with sheep.
String myString = "one fish, two fish, three fish";
String target = "fish";
String replacement = "sheep";
String newString = myString.replace(target, replacement);
// one sheep, two sheep, three sheep
replaceAll()
Use replaceAll() if you want to use a regular expression pattern.
Example 3
Replace any number with an x.
String myString = "__1_6____3__6_345____0";
String regex = "\\d";
String replacement = "x";
String newString = myString.replaceAll(regex, replacement);
// __x_x____x__x_xxx____x
Example 4
Remove all whitespace.
String myString = " Horse Cow\n\n \r Camel \t\t Sheep \n Goat ";
String regex = "\\s";
String replacement = "";
String newString = myString.replaceAll(regex, replacement);
// HorseCowCamelSheepGoat
See also
Documentation
replace(char oldChar, char newChar)
replace(CharSequence target, CharSequence replacement)
replaceAll(String regex, String replacement)
replaceFirst(String regex, String replacement)
Regular Expressions
Tutorial
List of patterns

The replace() method is overloaded to accept both a primitive char and a CharSequence as arguments.
Now as far as the performance is concerned, the replace() method is a bit faster than replaceAll() because the latter first compiles the regex pattern and then matches before finally replacing whereas the former simply matches for the provided argument and replaces.
Since we know the regex pattern matching is a bit more complex and consequently slower, then preferring replace() over replaceAll() is suggested whenever possible.
For example, for simple substitutions like you mentioned, it is better to use:
replace('.', '\\');
instead of:
replaceAll("\\.", "\\\\");
Note: the above conversion method arguments are system-dependent.

Both replace() and replaceAll() accepts two arguments and replaces all occurrences of the first substring(first argument) in a string with the second substring (second argument).
replace() accepts a pair of char or charsequence and replaceAll() accepts a pair of regex.
It is not true that replace() works faster than replaceAll() since both uses the same code in its implementation
Pattern.compile(regex).matcher(this).replaceAll(replacement);
Now the question is when to use replace and when to use replaceAll().
When you want to replace a substring with another substring regardless of its place of occurrence in the string use replace(). But if you have some particular preference or condition like replace only those substrings at the beginning or end of a string use replaceAll(). Here are some examples to prove my point:
String str = new String("==qwerty==").replaceAll("^==", "?"); \\str: "?qwerty=="
String str = new String("==qwerty==").replaceAll("==$", "?"); \\str: "==qwerty?"
String str = new String("===qwerty==").replaceAll("(=)+", "?"); \\str: "?qwerty?"

To throw more light with an example into how both are going to work for below code:
public static void main(String[] args)
{
String s = "My\\s aaab\\s is\\s aaab\\s name";
String s1 = s.replace("\\s", "c");
System.out.println(s1);
String s2 = s.replaceAll("\\s", "c");
System.out.println(s2);
}
Output:
Myc aaabc isc aaabc name
My\scaaab\scis\scaaab\scname
Explanation
s.replace replaces "\\s" sequence of characters with c. Hence, the output in first line.
s.replaceAll considers \\s as a regex rather(equivalent to space) and replaces spaces with c. \\s in String s is escaped with first \ encountered and becomes \s.
Intellij Idea is smart enough to notify you of the usage as well. If you take a closer look at below image, you will see the difference in interpretation by Intellij idea for replace and replaceAll usage.

String replace(char oldChar, char newChar)
Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
String replaceAll(String regex, String replacement
Replaces each substring of this string that matches the given regular expression with the given replacement.

Old thread I know but I am sort of new to Java and discover one of it's strange things. I have used String.replaceAll() but get unpredictable results.
Something like this mess up the string:
sUrl = sUrl.replaceAll( "./", "//").replaceAll( "//", "/");
So I designed this function to get around the weird problem:
//String.replaceAll does not work OK, that's why this function is here
public String strReplace( String s1, String s2, String s )
{
if((( s == null ) || (s.length() == 0 )) || (( s1 == null ) || (s1.length() == 0 )))
{ return s; }
while( (s != null) && (s.indexOf( s1 ) >= 0) )
{ s = s.replace( s1, s2 ); }
return s;
}
Which make you able to do:
sUrl=this.strReplace("./", "//", sUrl );
sUrl=this.strReplace( "//", "/", sUrl );

As alluded to in wickeD's answer, with replaceAll the replacement string is handled differently between replace and replaceAll. I expected a[3] and a[4] to have the same value, but they are different.
public static void main(String[] args) {
String[] a = new String[5];
a[0] = "\\";
a[1] = "X";
a[2] = a[0] + a[1];
a[3] = a[1].replaceAll("X", a[0] + "X");
a[4] = a[1].replace("X", a[0] + "X");
for (String s : a) {
System.out.println(s + "\t" + s.length());
}
}
The output of this is:
\ 1
X 1
\X 2
X 1
\X 2
This is different from perl where the replacement does not require the extra level of escaping:
#!/bin/perl
$esc = "\\";
$s = "X";
$s =~ s/X/${esc}X/;
print "$s " . length($s) . "\n";
which prints
\X 2
This can be quite a nuisance, as when trying to use the value returned by java.sql.DatabaseMetaData.getSearchStringEscape() with replaceAll().

From Java 9 there is some optimizations in replace method.
In Java 8 it uses a regex.
public String replace(CharSequence target, CharSequence replacement) {
return Pattern.compile(target.toString(), Pattern.LITERAL).matcher(
this).replaceAll(Matcher.quoteReplacement(replacement.toString()));
}
From Java 9 and on.
And Stringlatin implementation.
Which perform way better.
https://medium.com/madhash/composite-pattern-in-a-nutshell-ad1bf78479cc?source=post_internal_links---------2------------------

replace() method doesn't uses regex pattern whereas replaceAll() method uses regex pattern. So replace() performs faster than replaceAll().

To add to the already selected "Best Answer" (and others that are just as good like Suragch's), String.replace() is constrained by replacing characters that are sequential (thus taking CharSequence). However, String.replaceAll() is not constrained by replacing sequential characters only. You could replace non-sequential characters as well as long as your regular expression is constructed in such a way.
Also (most importantly and painfully obvious), replace() can only replace literal values; whereas replaceAll can replace 'like' sequences (not necessarily identical).

replace works on char data type but replaceAll works on String datatype and both replace the all occurrences of first argument with second argument.