Java String replaceFirst Method

The Java String replaceFirst method is one of the Java String Method, which is used to replace the first occurred sub string with newly specified string.

In this article we will show you, How to write String.replaceFirst method in Java Programming Language with example. Before we get into the example, the basic syntax of the String.replaceFirst is as shown below.

Java String ReplaceFirst Syntax

The Java Programming Language provides String.replaceFirst Method to replace the first sub string with user specified String.

Java String.replaceFirst Method will accept two string arguments, first argument (regexp) is the regular expression that represent a substring existing in the String_Object, and the second argument (Replacement) is the substring that you want to replace with.

public String replaceFirst(String Regexp, String Replacement); // It will return String 

//In order to use in program
String_Object.replaceFirst(String Regexp, String Replacement);

• String_Object: Please specify the valid string on which you want to perform Replacement.
• Regexp: Please specify the valid string that you want to change or regular expression that represents the String. Whatever you place here, Java String.replaceFirst method will be replace it by new string (Replacement)
• Replacement: Please specify the valid new string you want to insert into String_Object.

Java String ReplaceFirst Example

The String.replaceFirst in Java is used to replace the first occurred substring with user specified new string in a string object. In this Java program we will use the substring as the first argument. This may help you understand the basic functionality of the Java string.replaceFirst method.

JAVA CODE

// Java String.replaceFirst Example 
package StringFunctions;

public class ReplaceFirst {
	public static void main(String[] args) {
		String str = "Tutorials on Java Programming";
		String str1 = "We are abc working at abc company";
		
		String str2 = str.replaceFirst("a", "NEW");
		String str3 = str1.replaceFirst("a", "X");
		String str4 = str.replaceFirst("Java", "Java Script");
		String str5 = str1.replaceFirst("abc", "xyz");
		String str6 = str1.replaceFirst("abx", "xyz");

		System.out.println("After Replacing First String str = " + str2);
		System.out.println("After Replacing First String str1 = " + str3);
		System.out.println("After Replacing First String str = " + str4);
		System.out.println("After Replacing First String str1 = " + str5);
		System.out.println("After Replacing First String str1 = " + str6);
	}
}

OUTPUT

ANALYSIS

First we declared two String variables Str, Str1 and assigned corresponding values using following statement

String str = "Tutorials on Java Programming";
String str1 = "We are abc working at abc company";

Following statement will call the public String replaceFirst(String Regexp, String Replacement) method to find the substring ‘a’ and replace it with ‘x’. If you observe the above screenshot, Although ‘a’ sub string is repeated four times in Str variable, String.replaceFirst function is replacing the first occurrence

String str2 = str.replaceFirst("a", "NEW");

Following Java String replaceFirst statement will find the sub string ‘abc’ and replace it with sub string ‘xyz’ . If you observe the above screenshot, Although ‘abc’ sub string is repeated twice in Str variable, String.replaceFirst function is replacing the first occurrence

String str5 = str1.replaceFirst("abc", "xyz");

In the next line we are tried to replace the non-existing sub string ‘abx’ with sub string ‘xyz’ . From then above screenshot you can observe that, it is not replacing anything (String_Object is unchanged).

String str6 = str1.replaceFirst("abx", "xyz");

Lastly, we used the System.out.println statements to print the output.

Java String ReplaceFirst Example 2

The String.replaceFirst in Java is used to replace the existing substring with user specified new string in a string object. This Java program will help you to understand the use of regular expressions in Java string.replaceFirst method practically.

JAVA CODE

// Java String.replaceFirst Example 
package StringFunctions;

public class ReplaceFirst2 {
	public static void main(String[] args) {
		String str = "We are abc working at abc";
		String str1 = "Apple Cherry Apple";
		String strd = "Emp10s Emp20s Emp30s Emp40s";
		
		String str2 = str.replaceFirst("abc", "xyz");
		String str3 = str.replaceFirst("abc$", "xyz");
		String str4 = str1.replaceFirst("Apple", "Orange");
		String str5 = str1.replaceFirst("Apple$", "Orange");
		String str6 = str.replaceFirst("abc(.*)", "xyz");
		String str7 = str.replaceFirst("(.*)abc(.*)", "TutorialGateway.org");
		String str8 = strd.replaceFirst("Emp\\d\\ds", "Emp_ID 10 is Working in Sales Depat,");
		String str9 = strd.replaceFirst("Emp\\d\\ds$", ",Emp_ID 40 is Working in Sales Dept");

		System.out.println("After Replacing First Sub String in str = " + str2);
		System.out.println("After Replacing Last Sub String in str = " + str3);
		System.out.println("After Replacing First Sub String in str1 = " + str4);
		System.out.println("After Replacing Last Sub String in str1 = " + str5);
		System.out.println("After Replacing String str = " + str6);
		System.out.println("After Replacing String str = " + str7);
		System.out.println("After Replacing String strd = " + str8);
		System.out.println("After Replacing String strd = " + str9);
	}
}

OUTPUT

ANALYSIS

First we declared three String variables str, str1, strd and assigned corresponding data using following statement

String str = "We are abc working at abc";
String str1 = "Apple Cherry Apple";
String strd = "Emp10s Emp20s Emp30s Emp40s";

Following statement will call the public String replaceFirst(String Regexp, String Replacement) method to find the first occurred sub string ‘abc’ and replace it with sub string ‘xyz’ .

String str2 = str.replaceFirst("abc", "xyz");

Following Java String replaceFirst statement will find the last occurred sub string ‘abc’ and replace it with sub string ‘xyz’ . If you observe the above screenshot, Although ‘abc’ sub string is repeated twice in Str variable, String.replaceFirst function is replacing the last occurred

String str3 = str.replaceFirst("abc$", "xyz");

Following statement will find the sub string ‘abc’ and replace the ‘abc’ , the string after the ‘abc’ with sub string ‘xyz’ .

String str6 = str.replaceFirst("abc(.*)", "xyz");

This Java String replaceFirst statement will find the sub string ‘abc’ and replace the ‘abc’ , the string before it, string after the ‘abc’ with sub string ‘xyz’ .

String str7 = str.replaceFirst("(.*)abc(.*)", "TutorialGateway.org");

Following statement will find the first occurred sub string ‘Emp\\d\\ds’ and replace it with sub string ‘Emp_ID 10 is Working in Sales Depat,” . Here, \\d\\ means integer value in between the Emp and ds

String str8 = strd.replaceFirst("Emp\\d\\ds", "Emp_ID 10 is Working in Sales Depat,");

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