Swapping string in java

Swap Characters in String Java

Swap Characters in String Java | Java provides several built-in methods to swap characters in the string, it has made programmers easy by providing such methods. Let us see different ways available to swap characters in a string Java.

Example of swapping characters in a string Java:-

String str = "Know Program"; System.out.println(str); System.out.println(swap(str, 6, str.length() - 2));

Know P r ogr a m
Know P a ogr r m

Observe the code snippet, it has swapped the element in the 6th position ‘r’ with the element at the 10th position ‘a’ which is the length of the string – 2.

Here the swap() function is a user-defined function created for the user’s convenience. We will see the different ways to write this swap() method to swap characters in string Java.

How to Swap Two Characters in a String Java using toCharArray()

To swap two characters in a string in Java we can use the toCharArray() method available in the Java String class. Observe the below code, the swap is done between the first characters of each word that is 0th position is swapped with the 5th position. ‘K’ is swapped with ‘P’.

Program to Swap Two Characters in a String Java using toCharArray() Method

public class Main < public static char[] swap(String string, int i, int j) < char chr[] = string.toCharArray(); char temp = chr[i]; chr[i] = chr[j]; chr[j] = temp; return chr; >public static void main(String args[]) < String str = "Know Program"; System.out.println(str); System.out.println(swap(str, 0, 5)); >>

Swap Characters in String Java using substring()

Now, we will swap two characters in a string by using the substring() method. As we know the substring() method is a built-in method in java that returns a substring from the given string.

Program to Swap Characters in a String Java using substring()

public class Main < public static String swap(String string, int i, int j) < if (j == string.length() - 1) < return string.substring(0, i) + string.charAt(j) + string.substring(i + 1, j) + string.charAt(i); >return string.substring(0, i) + string.charAt(j) + string.substring(i + 1, j) + string.charAt(i)+ string.substring(j + 1, string.length()); > public static void main(String args[]) < String str = "Know Program"; System.out.println(str); System.out.println(swap(str, 0, 5)); >>

Swap Characters in String Java using StringBuilder

As we know the string is immutable which means we can not make any change once a string is created, on each and every modification a new String object will be created. Hence we can use the StringBuffer or StringBuilder class to modify the string elements. Now, let us see how to swap characters in string Java we will use StringBuilder Class.

Program to Swap Two Characters in a String Java Using StringBuilder

public class Main < static String stringSwap(String string, int i, int j) < StringBuilder sb = new StringBuilder(string); sb.setCharAt(i, string.charAt(j)); sb.setCharAt(j, string.charAt(i)); return sb.toString(); >public static void main(String args[]) < String str = "Know Program"; System.out.println(str); System.out.println(stringSwap(str, 0, 5)); >>

Observe all the above code works the same to swap characters in string Java but the methods and functions used are different.

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How to swap string characters in java?

Java provides several ways to swap characters in a String. Here are a few ways to do it, along with examples to help you understand the different methods.

Method 1: Using a char array

This method converts the String to a new character array, which can then be modified.

String input = "hello"; char[] inputArray = input.toCharArray();

• Step 2 — Use a temporary variable to store the value of the first character, then replace the first character with the second character, and then the second character with the temporary variable

This will effectively swap the two characters.

char temp = inputArray[0]; inputArray[0] = inputArray[1]; inputArray[1] = temp;

String output = String.valueOf(inputArray);

At this point, the output would be «jello»

Method 2: Using the substring() and concatenation methods

String input = "hello"; String firstChar = input.substring(0, 1); String secondChar = input.substring(1, 2);

String output = secondChar + firstChar + input.substring(2);

At this point, the output would be «jello»

Method 3: Using the CharSequence interface and the append() method

• Step 1 — Convert the String to a StringBuilder object, which is a class that implements the CharSequence interface

This allows you to use the append() method to change the characters within the String.

String input = "hello"; StringBuilder sb = new StringBuilder(input);

char temp = sb.charAt(0); sb.setCharAt(0, sb.charAt(1)); sb.setCharAt(1, temp);

String output = sb.toString();

At this point, the output would be «jello»

All the above methods, gives you a way to swap characters of a given string in Java. You can use any of the above method according to your convenience.

However, you should be mindful that, the above method only allow you to swap two characters. If you want to swap more than two characters, you will have to call these methods multiple times.

Sure, I can continue to explain more about the above methods and other ways to swap characters in a String in Java.

Another Method : Using the replace() method

String input = "hello"; StringBuilder sb = new StringBuilder(input);

char firstChar = input.charAt(0); char secondChar = input.charAt(1); int start = 0; int end = 1; sb.replace(start, end, Character.toString(secondChar)); sb.replace(start+1, end+1, Character.toString(firstChar));

String output = sb.toString();

You can use the above method in case of you have an index of characters you want to swap in the string.

All the above methods discussed are in-place swapping. Which means that the original input string is being modified. If you don’t want to modify the original string and create a new string instead, you can use any of the above methods and create a new string variable to store the output.

Conclusion

In conclusion, there are several ways to swap characters in a String in Java, including using a char array, substring() and concatenation, the CharSequence interface and the append() method, and the replace() method. Each of these methods has its own advantages and disadvantages, and the best method to use will depend on your specific use case. For example, if you’re working with a large string, using a char array and temporary variable might be more efficient than using the substring() and concatenation methods. On the other hand, the replace() method can be useful when you have an index of the characters you want to swap.

It is important to keep in mind that the methods described above are all in-place swapping, which means that the original input string is being modified. If you need to preserve the original string, make sure to create a new variable to store the output.

In summary, it’s recommended to understand the concept and performance of each method before choosing a method to swap the characters in a string.

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How to Swap Two Strings in Java without Third Variable

The simple approach to swap two strings in Java is by using a third variable. But, we can also swap two strings without using the third variable.

Swap Two Strings in Java using Third Variable

Here is the simple program to swap two strings using a third variable.

package net.javastring.strings; public class JavaSwapStrings < public static void main(String[] args) < String s1 = "Apple"; String s2 = "Banana"; System.out.printf("Before Swapping s1 = %s and s2 = %s.\n", s1, s2); String temp = s1; s1 = s2; s2 = temp; System.out.printf("After Swapping s1 = %s and s2 = %s.\n", s1, s2); >>

Before Swapping s1 = Apple and s2 = Banana. After Swapping s1 = Banana and s2 = Apple.

Swap Two Strings in Java without Third Variable

The idea is to use String concatenation and then substring() method to swap two strings without using any third variable.

package net.javastring.strings; public class JavaSwapStrings < public static void main(String[] args) < String s1 = "Apple"; String s2 = "Banana"; System.out.println(String.format("Before Swapping s1 = %s and s2 = %s.\n", s1, s2)); s1 = s1 + s2; // s1 = "AppleBanana"; s2 = s1.substring(0, s1.length()-s2.length()); // s2 = "AppleBanana".substring(0, 11-6) = "Apple" s1 = s1.substring(s2.length()); // s1 = "AppleBanana".substring(5) = "Banana" System.out.println(String.format("After Swapping s1 = %s and s2 = %s.\n", s1, s2)); >>

Notice the use of the String format() method. It works the same as System.out.printf() method.

References:

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Swapping string in java

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