StringBuilder Usage and Key Methods

StringBuilder(java.lang.StringBuilder)

What is StringBuilder? #

It is, as the name suggests, an object that builds Strings.

If you look at the API, the first line says 'A mutable sequence of characters'. String is an immutable object; modifying its value creates a new object, which consumes memory and time. However, using StringBuilder allows you to modify a mutable sequence, meaning only the value at the same memory address is changed, making it operate much faster. (It's like writing notes in a notepad.)

Constructors #

• StringBuilder sb = new StriugBuilder(); : Object declaration
• StringBuilder sb = new StringBuilder("You can directly insert a string");

Key Methods #

.append() #

Appends a string.

sb.append("bbb").append(4);

.insert(int offset, String str) #

Inserts str at the offset position.

sb.insert(2,"ccc");

.replace() #

Replaces the string located at the numeric indices received as the first and second parameters.

.replace(3,6,"yeye");

substring(int start, int end) #

Indexing. If there's one parameter, it indexes from that index to the end; if there are two, it indexes from the start to end - 1.

sb.substring(5);
sb.substring(3,7);

.deleteCharAt(int index) #

Deletes a single character at the specified index.

.delete(int start, int end) #

Deletes characters from start up to end - 1.

.toString() #

Converts to String.

.reverse() : Reverses the entire sequence of characters. #

.setCharAt(int index , String s) #

Changes the character at index to s.

.setLength(int len) #

• Adjusts string length
• If adjusted to be longer than the current string, it's padded with spaces.
• If adjusted to be shorter than the current string, remaining characters are deleted.

.trimToSize() #

• Adjusts the size of the char[] array storing the string to be equal to the current string length,
• Similar to how the String class's trim() removes leading/trailing spaces, this provides space trimming,
• Since the remaining size of the array is empty space, it can be seen as removing all trailing spaces from the string.

import java.lang.StringBuilder;

public class sb {
    public static void main(String[] args) throws IOException{
        StringBuilder sb = new StringBuilder("aaa");

        // Append string
        System.out.println(sb.append("bbb")); // aaabbb
        System.out.println(sb.append(4)); // aaabbb4

        // Insert string
        System.out.println(sb.insert(2, "ccc")); // aacccabbb4
        
        // Replace string, substitute string
        System.out.println(sb.replace(3, 6, "ye")); // aacyebbb4

        // Indexing, substring
        System.out.println(sb.substring(5)); // bbb4
        System.out.println(sb.substring(3, 7)); // yebb

        // Delete character
        System.out.println(sb.deleteCharAt(3)); // aacebbb4

        // Delete string
        System.out.println(sb.delete(3, sb.length())); // aac

        // Convert string
        System.out.println(sb.toString()); // aac

        // Reverse string
        System.out.println(sb.reverse()); // caa

        // Replace character, substitute character, change character
        sb.setCharAt(1, 'b');
        System.out.println(sb); // cba

        // Adjust string length
        sb.setLength(2);
        System.out.println(sb); // cb
    }
}