How to Use Java String Class replace() Method

Function Description

Java String class replace() method is used to replace all occurrences of the old character or sequence of characters respectively with new character or sequence of characters in the string.

  • If the specified old character or sequence of characters is not found in the sting, It will return the same string.

  • If the specified old character or sequence of characters finds in the sting, It will return a string resulting from replacing all occurrences of character(s).

  • If the specified old character or sequence of characters is null, It will throw NullPointerException.

  • If the specified new character or sequence of characters is null, It will throw NullPointerException.

Replace is an overloaded method in String class.

  1. One method is to replace the character

  2. Another  method is to replace the sequence of characters

For Example, String in which you want to replace the character/ sequence of characters is “lkarn rkplack method”, see what replace() method will return.

  1. “lkarn rkplack method”.replace(“g”,”e”) will return “lkarn rkplack method”

  2. “lkarn rkplack method”.replace(“k”,”e”) will return “learn replace method”

  3. “lkarn rkplack method”.replace(null,”e”) will throw NullPointer Exception

  4. “lkarn rkplack method”.replace(“k”, null) will throw NullPointer Exception

Method Signature

Method to replace character

public String replace(char oldChar, char newChar)

Method to replace the sequence of characters

public String replace(CharSequence target, CharSequence replacement)

Parameters

oldChar : A character of the string to be replaced in the string

newChar: New character to replace the old character in the string

target: The sequence of characters to be replaced in the string

replacement: Sequence of characters to replace the old sequence of characters in the string

Return Type

Replaced string after replacing old character(s) with the specified new character(s)

Exception

Throws NullPointerException if either of the specified parameters (oldChar, newChar, target or replacement ) is null

Example of Java String Class replace() Method

  1. Example of Java String Class replace() method to replace character
package com.java.test;
 
public class ExampleStringReplace {
 
    private void replaceCharacter(String str) {
 
         // replace character 4 with 6

          String relacedString = str.replace('4', '6');

          System.out.println("After replacing character 4 with 6 :" + relacedString);

    }
 
    public static void main(String[] args) {

          String str = "1234 1245 1256";

          System.out.println("Input String : " + str);

          System.out.println("");

          ExampleStringReplace exampleStringReplace = new ExampleStringReplace();

          exampleStringReplace.replaceCharacter(str);
 
     }

}


Output:

Input String : 1234 1245 1256
 
After replacing character 4 with 6 :1236 1265 1256

2.  Example of Java Sting Class replace() method to replace sequence of characters

package com.java.test;
 
public class ExampleStringReplace {
 
 
    private void replaceString(String str) {

          // replace charactersequence 12 with 67 in the given string

          String relacedString = str.replace("12", "67");

          System.out.println("After replace 12 with 67 : " + relacedString);

    }
 
    public static void main(String[] args) {

          String str = "1234 1245 1256";

          System.out.println("Input String : " + str);

          System.out.println("");

          ExampleStringReplace exampleStringReplace = new ExampleStringReplace();

          exampleStringReplace.replaceString(str);
 
    }

}

 
Output:

Input String : 1234 1245 1256
 
After replace 12 with 67 : 6734 6745 6756

3.  Example when NullPointerException is thrown

package com.java.test;
 
public class ExampleStringReplace {
 
 
    private void replaceString(String str) {

          // replace charactersequence 12 with 67 in the given string

          String relacedString = str.replace(null, "67");

          System.out.println("After replace 12 with 67 : " + relacedString);

    }
 
    public static void main(String[] args) {

          String str = "1234 1245 1256";

          System.out.println("Input String : " + str);

          System.out.println("");

          ExampleStringReplace exampleStringReplace = new ExampleStringReplace();

          exampleStringReplace.replaceString(str);
 
    }

}


Output:

Input String : 1234 1245 1256
 

Exception in thread "main" java.lang.NullPointerException

    at java.lang.String.replace(String.java:2239)

    at com.java.test.ExampleStringReplace.replaceString(ExampleStringReplace.java:8)

    at com.java.test.ExampleStringReplace.main(ExampleStringReplace.java:17)

Other Methods of String Class

SequenceMethodDescription
1char charAt(int index)This method is used to return the character of the string at specified index. First character is at index 0 while last is at string length-1 . StringIndexOutOfBounds Exception is thrown if valid index value is not passed.
2int length()Returns the number of characters count  in  a string.
3static String format(String format, Object… args)Return the formatted String. It is a static method and formats the string as per passing format and argument(s).
4static String format(Locale l, String format, Object… args)Return the formatted String. It is a static method and formats the string as per passing format and argument(s) and locale.
5String substring(int beginIndex)Returns substring from the given index position to the end index of the string.
6String substring(int beginIndex, int endIndex)Returns substring from the specified begin index to the specified end index.
7boolean contains(CharSequence s)Returns boolean value(true/false). It searches the given sequence of characters within the string and returns true/false accordingly. Characters will be case sensitive while searching in string.
8static String join(CharSequence delimiter, CharSequence… elements)Returns joined string. This method joins each passing String using the specified delimiter. It is a static method.
9static String join(CharSequence delimiter, Iterable<? extends CharSequence> elements)Returns the joined string. This method joins each passing string object of an iterate object using the specified delimiter and returns the concatenated string. It is a static method.
10boolean equals(Object another)Returns boolean value(true/false). It checks the equality of string with the passing object.
11boolean isEmpty()Returns boolean value(true/false). It returns true if the string is empty otherwise returns false.
12String concat(String str)Returns the concatenating string. It concatenates the passing string at the end of the string.
13String replaceAll(String regex, String replacement)Returns the replaced string. It replaces all occurrences of the sequence of characters with the given replacement string that are matching with the given regular expression.
14String replaceFirst(String regex, String replacement)Returns the replaced string. It replaces the first matching sequence of characters with the replacement string that matches with the given regular expression.
15static boolean equalsIgnoreCase(String another)Returns the boolean (true/false) value. It compares the passing string with string by ignoring the case. It  compares the content irrespective of lowercase or uppercase of the character(s).
16String[] split(String regex)Returns the array of strings resulting from splitting of the string     around matches of the given regular expression. String is breaked into strings from all  the matching regular expressions.
17String[] split(String regex, int limit)Returns the array of strings resulting from splitting of the string     around matches of the given regular expression. It breaks the string from all the matching regular expression upto the given limit.
18String intern()Returns an interned string. This method helps to compare two objects using == operator and checks in a string constant pool. it is faster for comparison.
19int indexOf(int ch)Returns the index value of first occurrence of the specified character within the string
20int indexOf(int ch, int fromIndex)Returns the index value of first occurrence of the specified character from the substring starting from specified index
21int indexOf(String substring)Returns the index value of first occurrence of the specified substring within the string.
22int indexOf(String substring, int fromIndex)Returns the index value of the first occurrence of the specified string within the substring starting from specified index to end of the string index.
23int lastIndexOf(int ch)Returns the index value of last occurrence of the specified character
24int lastIndexOf (int ch, int fromIndex)Returns the index value of last occurrence of the specified character, search starts at given fromIndex. 
25int lastIndexOf (String str)Returns the index value of last occurrence of the specified string.
26int lastIndexOf (String str, int fromIndexReturns the index value of last occurrence of the specified string, searches start from given fromIndex
27String toLowerCase()Returns all the characters of the string in lowercase .
28String toLowerCase(Locale l)Returns all the characters of the string in lowercase using specified locale.
29String toUpperCase()Returns all the characters of the string in uppercase.
30String toUpperCase(Locale l)Returns all the characters of the string in uppercase using specified locale.
31String trim()Returns the string after removing the white space from the beginning and end of the string.
32static String valueOf(int value)Return the converted string. It converts the objects and all primitive types of values into string. It is a static method.

In this article, we learned all about the replace() method of Java String class with examples. Apart from replace() method we got an idea about other String methods too. We will come up with more articles explaining other String methods with examples. For more details please click on the respective methods link.

This article was written by Renu Singh

14+ Years of experience in various phases of the software development life cycle. Specialties: Java/J2EE, Struts, Hibernate, JSF, JSP, Servlets, AJAX, Oracle, Oracle Knowledge, SQL Server 2000, DB2, EJB3.0. Companies Worked For: 1) Tata Consultancy Services 2) Infogain 3) TS Infotech 4) Daffodil Software Ltd.

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