Java Program to Replace First Character Occurrence in a String

Write a Java Program to replace First Character Occurrence in a String with an example. In this Java replace first Occurrence of a Character example, we compare each character in repstCharStr string with the replace_ch. If they are equal, we assigned new_ch in that index position followed by break statement to exit from the While loop.

import java.util.Scanner;

public class ReplaceFirstCharOccur1 {
	private static Scanner sc;
	public static void main(String[] args) {
		String repstCharStr;
		char replace_ch, new_ch;
		int i = 0;
		
		sc= new Scanner(System.in);

		System.out.print("\nPlease Enter any String =  ");
		repstCharStr = sc.nextLine();
		
		System.out.print("\nEnter the Character to Replace =  ");
		replace_ch = sc.next().charAt(0);
		
		System.out.print("\nEnter the New Character =  ");
		new_ch = sc.next().charAt(0);
		
		char[] repstCharArr = repstCharStr.toCharArray();
		while(i < repstCharArr.length)
		{
			if(repstCharArr[i] ==  replace_ch) {
				repstCharArr[i] = new_ch;
				break;
			}
			i++;
		}
		System.out.format("\nThe Final String after replacing %c with %c = ", replace_ch, new_ch);
		System.out.print(repstCharArr);
	}
}

OUTPUT

Java Program to Replace First Character Occurrence in a String Example 2

This Java replace the first occurrence of a character example is the same as the above, and we replaced the While loop with For Loop.

import java.util.Scanner;

public class ReplaceFirstCharOccur2 {
	private static Scanner sc;
	public static void main(String[] args) {
		String repstCharStr;
		char replace_ch, new_ch;
		
		
		sc= new Scanner(System.in);

		System.out.print("\nPlease Enter any String =  ");
		repstCharStr = sc.nextLine();
		
		System.out.print("\nEnter the Character to Replace =  ");
		replace_ch = sc.next().charAt(0);
		
		System.out.print("\nEnter the New Character =  ");
		new_ch = sc.next().charAt(0);
		
		char[] repstCharArr = repstCharStr.toCharArray();
		for(int i = 0; i < repstCharArr.length; i++)
		{
			if(repstCharArr[i] ==  replace_ch) {
				repstCharArr[i] = new_ch;
				break;
			}
		}
		System.out.format("\nThe Final String after replacing %c with %c = ", replace_ch, new_ch);
		System.out.print(repstCharArr);
	}
}

OUTPUT

The replaceFirst is a string function that replaces the first occurrence of a charter with the new character.

import java.util.Scanner;

public class ReplaceFirstCharOccur3 {
	private static Scanner sc;
	public static void main(String[] args) {
		String repstCharStr;
		String replace_ch, new_ch;
		
		sc= new Scanner(System.in);

		System.out.print("\nPlease Enter any String =  ");
		repstCharStr = sc.nextLine();
		
		System.out.print("\nEnter the Character to Replace =  ");
		replace_ch = sc.nextLine();
		
		System.out.print("\nEnter the New Character =  ");
		new_ch = sc.nextLine();
		
		String x = repstCharStr.replaceFirst(replace_ch, new_ch);
		
		System.out.format("\nThe Final String after replacing %s with %s = %s", 
				replace_ch, new_ch, x);
	}
}

RESULT

We can use the Java String substring function to replace the first character occurrence. In this Java program, repstCharStr.substring(0, i) returns substring up to the index position of the replace_ch character. Next, we added the new_ch to it. Then, we used another substring repstCharStr.substring(i + 1, repstCharStr.length() to concat string from i to the end of that string.

import java.util.Scanner;

public class ReplaceFirstCharOccur4 {
	private static Scanner sc;
	public static void main(String[] args) {
		String repstCharStr;
		String replace_ch, new_ch;
		
		sc= new Scanner(System.in);

		System.out.print("\nPlease Enter any String =  ");
		repstCharStr = sc.nextLine();
		
		System.out.print("\nEnter the Character to Replace =  ");
		replace_ch = sc.nextLine();
		
		System.out.print("\nEnter the New Character =  ");
		new_ch = sc.nextLine();
		
		int i = repstCharStr.indexOf(replace_ch);
		String x = repstCharStr.substring(0, i) + new_ch +
					repstCharStr.substring(i + 1, repstCharStr.length() );
	
		System.out.format("\nThe Final String after replacing %s with %s = %s", 
				replace_ch, new_ch, x);
	}
}

RESULT