string set char at java

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StringBuilder setCharAt() in Java with Examples

The setCharAt(int index, char ch) method of StringBuilder class is used to set the character at the position index passed as ch. This method changes the old sequence to represents a new sequence which is identical to old sequence only difference is a new character ch is present at position index. The index argument must be greater than or equal to 0, and less than the length of the String contained by StringBUilder object. Syntax:

Parameters: This method accepts two parameters:

Returns: This method returns nothing. Exception: If the index is negative, greater than length() then IndexOutOfBoundsException.

Below programs illustrate the java.lang.StringBuilder.setCharAt() method: Example 1:

Example 3: When negative index is passed:

References: https://docs.oracle.com/javase/10/docs/api/java/lang/StringBuilder.html#setCharAt(int, char)

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Replace a character at a specific index in a string?

I'm trying to replace a character at a specific index in a string.

What I'm doing is:

This gives an error. Is there any method to do this?

9 Answers 9

String are immutable in Java. You can't change them.

You need to create a new string with the character replaced.

Or you can use a StringBuilder:

Turn the String into a char[], replace the letter by index, then convert the array back into a String.

String is an immutable class in java. Any method which seems to modify it always returns a new string object with modification.

If you want to manipulate a string, consider StringBuilder or StringBuffer in case you require thread safety.

I agree with Petar Ivanov but it is best if we implement in following way:

As previously answered here, String instances are immutable . StringBuffer and StringBuilder are mutable and suitable for such a purpose whether you need to be thread safe or not.

There is however a way to modify a String but I would never recommend it because it is unsafe, unreliable and it can can be considered as cheating : you can use reflection to modify the inner char array the String object contains. Reflection allows you to access fields and methods that are normally hidden in the current scope (private methods or fields from another class...).

You can overwrite a string, as follows:

Note that the string myName occurs on both lines, and on both sides of the second line.

Therefore, even though strings may technically be immutable, in practice, you can treat them as editable by overwriting them.

1 I haven't downvoted your answer but I must admit I have a problem with the term "overwrite" (though I think we agree on the concept behind). The object itself remains unchanged. You just make your variable reference another object. By the way it you be interesting to mention that you create at least four String instances in your example. – C.Champagne Oct 20, 2015 at 12:47

First thing I should have noticed is that charAt is a method and assigning value to it using equal sign won't do anything. If a string is immutable, charAt method, to make change to the string object must receive an argument containing the new character. Unfortunately, string is immutable. To modify the string, I needed to use StringBuilder as suggested by Mr. Petar Ivanov.

You can overwrite on same string like this

where index = the index of char to replacement. index+1 to add rest of your string

Output : domaxokz

Not the answer you're looking for? Browse other questions tagged java string replace indexing character or ask your own question .

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2297/how-do-i-replace-character-from-string-at-specific-indexes

How do I replace character from string at...

How do I replace character from string at specific indexes

I need to replace character from string at specific index.

This is how I am trying to do it:

This gives an error. Is there any method to do this?

Your comment on this question:

2 answers to this question., your answer.

String are immutable in Java. You can't change them.

You need to create a new string with the character replaced.

String myName = "domanokz" ; String newName = myName . substring ( 0 , 4 )+ 'x' + myName . substring ( 5 );

Or you can use a StringBuilder:

StringBuilder myName = new StringBuilder ( "domanokz" ); myName . setCharAt ( 4 , 'x' );

System . out . println ( myName );

ask related question

Your comment on this answer:

You could turn the String into a char[] , replace the letter by index, then convert the array back into a String.

Hope this helps!

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Replace a character at a specific index in a String in Java

This post will discuss how to replace a character at a specific index in a Java String.

The string is an immutable class in Java. That means we cannot make any change in the String object. The only feasible solution is to create a new String object with the replaced character. There are several ways to replace a character at a specific index in a string:

1. Using substring() method

We can use String.substring(int, int) method to partition the string into two halves consisting of substring before and after the character to be replaced. Once we have isolated the character to be replaced, we can use the concatenation operator to build the final string, as shown below:

Download Run Code

Output: Techie_Delight

2. Using StringBuilder

The recommended solution is to use mutable class StringBuilder to efficiently replace a character at a specific index in a string in Java. Alternatively, we can also use a slower StringBuffer class if thread safety is required.

3. Using toCharArray() method

Another plausible way of replacing character at the specified index in a string is using a character array that can be modified easily. The idea is to convert the given string to a character array using its toCharArray() method and then replace the character at the given index in the character array. Finally, convert the character array back into a string using String.valueOf(char[]) method.

4. Using Reflection

We have seen that we cannot make any change in the String object as string is immutable in Java. However, there is a way to modify a string using reflection. Reflection in Java allows code to perform illegal operations such as accessing and manipulating private fields and methods.

We know that string internally uses a character array that is final and private to the class. Although not recommended, reflection can easily modify that private character array.

That’s all about replacing a character at a specific index in a Java String.

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Java.lang.StringBuffer.setCharAt() Method

The java.lang.StringBuffer.setCharAt() method sets the character at the specified index to ch . This sequence is altered to represent a new character sequence that is identical to the old character sequence, except that it contains the character ch at position index .

Declaration

Following is the declaration for java.lang.StringBuffer.setCharAt() method

index − This is the index of the character to modify.

ch − This is the new character.

Return Value

This method does not return any value.

IndexOutOfBoundsException − if index is negative or greater than or equal to length().

The following example shows the usage of java.lang.StringBuffer.setCharAt() method.

Let us compile and run the above program, this will produce the following result −

Replace a Character at a Specific Index in a String in Java

Last modified: October 29, 2019

Java String

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In this quick tutorial, we’ll demonstrate how to replace a character at a specific index in a String in Java.

We’ll present four implementations of simple methods that take the original String, a character, and the index where we need to replace it.

2. Using a Character Array

Let's begin with a simple approach, using an array of char.

Here, the idea is to convert the String to char[] and then assign the new char at the given index. Finally, we construct the desired String from that array.

This is a low-level design approach and gives us a lot of flexibility.

3. Using the substring Method

A higher-level approach is to use the substring() method of the String class.

It will create a new String by concatenating the substring of the original String before the index with the new character and substring of the original String after the index:

4. Using StringBuilder

We can get the same effect by using StringBuilder . We can replace the character at a specific index using the method setCharAt():

5. Conclusion

In this article, we focused on several ways of replacing a character at a specific index in a String using Java .

String instances are immutable, so we need to create a new string or use StringBuilder to give us some mutability.

As usual, the complete source code for the above tutorial is available over on GitHub .

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COMMENTS

Replace a character at a specific index in a String in Java
Unlike String Class, the StringBuilder class is used to represent a mutable string of characters and has a predefined method for change a
StringBuilder setCharAt() in Java with Examples
The setCharAt(int index, char ch) method of StringBuilder class is used to set the character at the position index passed as ch.
Replace a character at a specific index in a string?
String are immutable in Java. You can't change them. You need to create a new string with the character replaced. String myName = "domanokz"
How do I replace character from string at specific indexes
String are immutable in Java. You can't change them. You need to create a new string with the character replaced. String myName =
Java StringBuilder setCharAt() Method with Examples
The setCharAt(int index, char ch) method of Java StringBuilder class is used to set the specified character at the given index. The specified character
Java String charAt() method
The Java String class charAt() method returns a char value at the given index number. The index number starts from 0 and goes to n-1, where n is the length of
Replace a character at a specific index in a String in Java
Replace a character at a specific index in a String in Java · 1. Using substring() method. We can use String. · 2. Using StringBuilder. The recommended solution
Java StringBuilder setCharAt() Method
The Java StringBuilder setCharAt() method, is used to add/insert the character at the specified index in a StringBuilder object. The index refer to the
Java.lang.StringBuffer.setCharAt() Method
The java.lang.StringBuffer.setCharAt() method sets the character at the specified index to ch. This sequence is altered to represent a new character
Replace a Character at a Specific Index in a String in Java
replaceCharUsingCharArray · char[] chars = str.toCharArray(); chars[index] = ch; return String.valueOf(chars); } ; replaceChar · return str.