Replace part of a string between indexes in Java [closed]

Question

Try below code. With help of StringBuffer you do replacement. StringBuffer replace java docs

public static void main(String[] args) {

        StringBuffer buf = new StringBuffer("123456789");

        int start = 3;
        int end = 6;
        buf.replace(start, end, "foobar"); 
        System.out.println(buf);

    }

}

After running above program below will be out put.

123foobar789

Demo

Firstly, you cannot do it¹, since a String is immutable in java.

However, you can create a new String object with the desired value, using the String#substring() method (for example):

String s = "123456789";
String newString = s.substring(0, 3) + "foobar" + s.substring(3+3);
System.out.println(newString);

---

If you do want to achieve it efficiently, you could avoid creating some intermediate strings used by the concatinating and substring() method.

String s = "123456789";
StringBuilder sb = new StringBuilder();
char[] buff = s.toCharArray();
sb.append(buff , 0, 3).append("foobar");
sb.append(buff,3+3,buff.length -(3+3));
System.out.println(sb.toString());

However, if it is not done in a very tight loop - you should probably ignore it, and stick with the first and more readable solution.

---

(1) not easily anyway, it can be done with reflection - but it should be avoided.

If there is no repetition of given substring then try this.

String s ="123456789";
s = s.replace(s.substring(3,6), "foobar");

If there is repetition of given substring then try this.

String s ="123123123";
s= s.substring(0,3) + "foobar" + s.substring(6,s.length());