When Should I Choose StringBuilder Over String?

Why Use StringBuilder Over String?

String, a powerful class in Java, allows appending. However, despite String's capabilities, a distinct class called StringBuilder emerged for specific reasons.

Immutability vs. Mutability

The fundamental difference lies in the nature of String and StringBuilder. String is immutable, meaning its internal state cannot change. Each operation performed on a String results in a new object being created. This can be inefficient for operations involving repeated concatenations.

Conversely, StringBuilder is mutable. When you append to a StringBuilder, it modifies the internal char array instead of creating a new object. This significantly improves performance for string manipulation.

Efficiency

Consider the following code:

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

This code snippet would create 500 new String objects, which is inefficient. Using StringBuilder instead:

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

results in only one StringBuilder object being modified, leading to significant performance gains.

Optimal Usage

While StringBuilder is more efficient for concatenations, it's important to note that the compiler automatically translates certain String expressions to avoid creating multiple objects. For instance:

String d = a + b + c; // implicit use of StringBuilder

If thread safety is a concern, consider using StringBuffer, which provides synchronized methods.

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