Why Use StringBuilder When String Has Append Methods?

Why StringBuilder Despite String's Append Capabilities?

Java's String class offers methods for appending content, but it's immutable, meaning it cannot modify its internal state. Consequently, each append operation creates a new String object, an inefficient process for repetitive appending.

Enter StringBuilder

StringBuilder addresses this limitation by being mutable. Its append method modifies its underlying character array, eliminating the need to generate new objects with each append. This efficiency is particularly valuable in loops and complex string manipulations.

Comparison:

Consider the following example:

String str = "";
for (int i = 0; i < 500; i++) {
    str += i;
}

This code creates 500 new String objects, incurring significant overhead. In contrast, using StringBuilder:

StringBuilder sb = new StringBuilder();
for (int i = 0; i < 500; i++) {
    sb.append(i);
}

augments the same String object without creating new ones.

Automatic Conversion

The compiler automatically translates concatenation expressions (e.g., "String d = a b c") into StringBuilder-based operations:

String d = new StringBuilder(a).append(b).append(c).toString();

Other Options:

In addition to StringBuilder, Java provides StringBuffer, which has synchronized methods. It's primarily useful in multi-threaded scenarios where thread-safe access is necessary.

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