How do I append and replace content of a StringBuffer?

A StringBuffer is like a String, but can be modified. StringBuffer are safe for use by multiple threads. The methods are synchronized where necessary so that all the operations on any particular instance behave as if they occur in some serial order that is consistent with the order of the method calls made by each of the individual threads involved.

As of release JDK 1.5, this class has been supplemented with an equivalent class designed for use by a single thread, StringBuilder. The StringBuilder class should generally be used in preference to this one, as it supports all of the same operations but it is faster, as it performs no synchronization.

package org.kodejava.example.lang;

public class StringBufferAppendReplace {
    public static void main(String[] args) {
        StringBuffer quote = new StringBuffer("an apple ");
        char a = 'a';
        String day = " day";
        StringBuffer sentences = new StringBuffer(" keep the doctor away");

        // Append a character into StringBuffer
        quote.append(a);
        System.out.println("quote = " + quote.toString());

        // Append a string into StringBuffer
        quote.append(day);
        System.out.println("quote = " + quote.toString());

        // Append another StringBuffer
        quote.append(sentences);
        System.out.println("quote = " + quote.toString());

        // Replace a sub string from StringBuffer starting
        // from index = 3 to index = 8
        quote.replace(3, 8, "orange");
        System.out.println("quote = " + quote.toString());
    }
}

Here is our program output:

quote = an apple a
quote = an apple a day
quote = an apple a day keep the doctor away
quote = an orange a day keep the doctor away

How do I replace characters in string?

package org.kodejava.example.lang;

public class StringReplace {
    public static void main(String[] args) {
        String text = "The quick brown fox jumps over the lazy dog";
        System.out.println("Before: " + text);

        // The replace method replace all occurrences of character
        // 'o' with 'u' and returns a new string object.
        text = text.replace('o', 'u');
        System.out.println("After : " + text);
    }
}

The result of the code snippet:

Before: The quick brown fox jumps over the lazy dog
After : The quick bruwn fux jumps uver the lazy dug

How do I create a repeated sequence of character?

This example show you how to create a repeated sequence of characters. To do this we use the Arrays.fill() method. This method fills an array of char with a character.

package org.kodejava.example.util;

import java.util.Arrays;

public class RepeatCharacterExample {
    public static void main(String[] args) {
        char c = 'x';
        int length = 10;

        // creates char array with 10 elements
        char[] chars = new char[length];

        // fill each element of chars array with 'x'
        Arrays.fill(chars, c);

        // print out the repeated 'x'
        System.out.println(String.valueOf(chars));
    }
}

As the result you get the x character repeated 10 times.

xxxxxxxxxx

For one liner code you can use the following code snippet, which will give you the same result.

new String(new char[10]).replace('\0', 'x');

Or

String.join("", Collections.nCopies(10, "x"));