String Replaceall() Event - How To Supersede All Characters In Addition To Substring From String

You tin supersede all occurrence of a unmarried character, or a substring of a given String inwards Java using the replaceAll() method of java.lang.String class. This method besides allows you lot to specify the target substring using the regular expression, which agency you lot tin exercise this to remove all white space from String. The replaceAll() role is real useful, versatile in addition to powerful method in addition to every bit a Java developer, you lot must know close it. Even though Java provides separate methods for replacing characters in addition to replacing substring, you lot tin create all that simply past times using this unmarried method. The replaceAll() method replaces each substring of this string (the String on which it is called) that matches the given regular human face amongst the given replacement. It internally uses classes similar Pattern in addition to Matcher from java.util.regex packet for searching in addition to replacing matching characters or substring.

Since String is immutable inwards Java it cannot move changed, thus this method returns a novel modified String. If you lot desire to exercise that String you lot must shop it dorsum on the relevant variable. Many developers forget to shop the trial of replaceAll() method dorsum in addition to think that the master copy String is modified, which is incorrect in addition to creates simply about of the most mutual but difficult to notice bugs inwards Java.

This concept is non simply relevant for the replaceAll() method but other methods of java.lang.String shape which does String manipulation e.g. trim(), split(), join() or concat() methods.

In this tutorial, I'll exhibit you lot 3 examples of using the replaceAll() method inwards Java for replacing characters, substring in addition to using the regular human face for advanced notice in addition to supersede task.

String replaceAll() Example inwards Java

Here is a sample Java programme which volition demonstrate how to exercise the replaceAll method inwards Java for replacing a single character, a substring in addition to using a regular human face for sophisticated notice in addition to replace, much similar how you lot create inwards VI editor inwards Linux.

In the foremost instance of replaceAll(), I bring shown you lot how to supersede all occurrence of a unmarried grapheme inwards String. This is besides 1 of the mutual String coding questions but at that topographic point you lot demand to solve the employment without using the replaceAll() method.

Remember, fifty-fifty though replaceAll() allows you lot to supersede a unmarried character, you lot cannot exceed a char value to this method every bit it expects String. As a workaround, you lot demand to exceed a unmarried grapheme String e.g. "a", "b" etc.


You should besides remember, unmarried quotes are used for character literals inwards Java in addition to double quotes are used for String literals inwards Java e.g. 'a' is a char variable but "a" is a String variable.

String bestseller = "clean code"; String option = bestseller.replaceAll("e", "a");  System.out.println("orginal string: " + bestseller); // impress build clean code System.out.println("replaced string: " + alternative); // impress claan coda

In the minute instance of the replaceAll() method, I bring shown you lot how to supersede all occurrence of a substring inwards Java. Again it's uncomplicated simply exceed the target in addition to replacement to the replaceAll() method, it is real similar to how you lot exercise the replace(CharSequence target, CharSequence replacement) method every bit demonstrated here.

String sample = "123 123 123 123 321"; String replaced = sample.replaceAll("123", "111"); System.out.println("orginal string: " + sample); // impress 123 123 123 123 321 System.out.println("replaced string: " + replaced); // impress 111 111 111 111 321

The 3rd 1 is the most interesting example, which replaces all whitespaces from String inwards Java.It uses a regular expression "\\s+" to convert String "Java is great" into "Javaisgreat". Since the foremost declaration to the replaceAll() method is a regular human face String, it's possible to perform such sophisticated notice supersede role inwards Java.

// 3rd instance - replacement using regular expression // the foremost declaration you lot exceed its regular expression // you lot tin exercise this to supersede all white infinite from // string every bit shown below String textWithWhitespace = "Java is great"; String changed = textWithWhitespace.replaceAll("\\s+", ""); System.out.println("orginal string: " + textWithWhitespace); System.out.println("replaced string: " + changed);

If you lot are curious close what does "\\s+" regex blueprint does so here is a brusque explanation.

Java String replaceAll() Example

Here is our consummate Java program, which includes all the 3 examples nosotros bring discussed above. You tin write this programme yourself in addition to run it to run across the result. You tin farther heighten this programme past times bespeak the user to movement into input String in addition to the grapheme or substring to move replaced inwards ascendance prompt. You tin exercise Scanner to read input from the ascendance prompt in addition to so exercise the same logic every bit discussed hither for search in addition to replace.

public class Main {    public static void main(String args[]) {      // 1st instance - replacing all occurrence of a grapheme inwards String     // you lot tin supersede unmarried grapheme but you lot cannot exceed a char     // to this replace() function, it await a string, so you lot should     // exceed a unmarried grapheme string every bit shown below     String bestseller = "clean code";     String option = bestseller.replaceAll("e", "a");      System.out.println("orginal string: " + bestseller);     System.out.println("replaced string: " + alternative);      // 2d instance - replacing all occurrence of a substring     String sample = "123 123 123 123 321";     String replaced = sample.replaceAll("123", "111");     System.out.println("orginal string: " + sample);     System.out.println("replaced string: " + replaced);      // 3rd instance - replacement using regular expression     // the foremost declaration you lot exceed its regular expression     // you lot tin exercise this to supersede all white infinite from     // string every bit shown below     String textWithWhitespace = "Java is great";     String changed = textWithWhitespace.replaceAll("\\s+", "");     System.out.println("orginal string: " + textWithWhitespace);     System.out.println("replaced string: " + changed);    }  }  Output master copy string: build clean code replaced string: claan coda master copy string: 123 123 123 123 321 replaced string: 111 111 111 111 321 master copy string: Java is nifty replaced string: Javaisgreat

You tin run across from the output inwards the foremost example, grapheme 'e' is successfully replaced past times the missive of the alphabet 'a' and inwards the minute example, substring "123" is replaced past times "111", in addition to inwards the 3rd example, all whitespace is removed past times replacing them amongst empty String.

If you lot desire to acquire to a greater extent than close regular human face in addition to Java fundamentals, I propose you lot reading either Head First Java or Core Java past times Cay S. Horstmann, both are nifty books to empathise basic concepts similar this.

Important points close replaceAll() method

Here are simply about of the of import things to know in addition to retrieve close the String.replaceAll() method inwards Java:

1) An invocation of this method of the shape str.replaceAll(regex, replacement) yields just the same trial every bit the expression

java.util.regex.Pattern.compile(regex).matcher(str).replaceAll(replacement)

2) If the regular expression's syntax is invalid in addition to the String.replaceAll()  method throws PatternSyntaxException.

3) This method is available from Java 1.4 so you lot tin exercise it on Java v every bit well.

4) Even though you lot tin exercise the replaceAll() method to supersede a unmarried grapheme or a substring, you lot should e'er exceed a String to it. You cannot exceed the grapheme to it, that would move compile fourth dimension fault every bit shown below:

"string".replaceAll('t', 'd'); // compile fourth dimension error

5) The foremost declaration to this method is a regular human face String, so metacharacters bring unlike important e.g. "\\s+" means to supersede whatsoever whitespace upwards to whatsoever length.


That's all close how to exercise the replaceAll() method of java.lang.String class to supersede characters in addition to substring inwards Java. The most of import affair to retrieve close the replaceAll() method is that it supports regular human face which allows you lot to perform sophisticated notice in addition to supersede programmatically, much similar how create you lot create inwards VI editor. If you lot desire to acquire to a greater extent than close methods of String class, you lot tin farther read Java: How to Program past times Dietel in addition to Dietel.

Further Learning
Data Structures in addition to Algorithms: Deep Dive Using Java
Java Fundamentals: The Java Language
Complete Java Masterclass

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