Java StringBuilder Demystified

#java #cod #tutorial #leadership

Let's understand what makes every lead developer say that you should know how to create your own StringBuilder if you plan to modify your strings.
And most of all - what is the difference between string concatenation vs using this pattern.

Simply put what we want to do is - an efficient management of space and performance.

This is the simplest of all the implementations with core characteristics of a StringBuilder

.append()
.length()
.toString()

MyStringBuilder

import java.util.Arrays;

public class MyStringBuilder {

    private static final int INIT_CAPACITY = 16;
    private static final float LOAD_FACTOR = 0.75f;
    private static final int MULTIPLIER = 2;

    private int currentCapacity = INIT_CAPACITY;

    // store the total number of characters in our string builder
    private int count;

    // storage area for our characters
    private char[] chars;

    public MyStringBuilder() {
        chars = new char[INIT_CAPACITY];
    }

    public MyStringBuilder(String str) {
        this();
        append(str);
    }

    public MyStringBuilder append(String newStr) {

        final int length = newStr.length();

        // check if resized or not
        boolean inflated = ensureCapacity(length);

        if (inflated) {
            final char[] newBuffer = new char[currentCapacity];
            // copy current content
            System.arraycopy(chars, 0, newBuffer, 0, count);
            // copy new content
            System.arraycopy(newStr.toCharArray(), 0, newBuffer, count, length);

            // update the store array
            chars = newBuffer;
        } else {
            // add the new content to the remaining array space
            System.arraycopy(newStr.toCharArray(), 0, chars, count, length);
        }

        // update the count of chars
        count += length;

        return this;
    }

    private boolean ensureCapacity(int newLength) {
        boolean isInflated = false;
        // ensure the new length is properly accommodated
        while (Float.compare((float) (count + newLength) / currentCapacity, LOAD_FACTOR) >= 0) {
            currentCapacity *= MULTIPLIER;
            isInflated = true;
        }

        return isInflated;
    }

    public int length() {
        return count;
    }

    @Override
    public String toString() {
        return new String(Arrays.copyOfRange(chars, 0, count));
    }
}

public class MyStringBuilderDriver {

    public static void main(String[] args) {

        var sb = new MyStringBuilder();

        sb.append("Hi").append(" ");
        sb.append("Saurabh").append(",").append(" ");
        sb.append("how are you today ?");

        System.out.println(sb);
        System.out.println(sb.length());
    }
}