Terence

If you are dynamically generating strings in your Java program, one of the best things you can do for your program is to build your string using a StringBuilder or StringBuffer, as opposed to using a regular old String.

The reason for this? In Java, strings are immutable, and every time you concatenate a string that the program hasn’t seen before, a new string object is created and stored in the heap. This means the whole process involves a lot of reading from and writing to the memory. The StringBuilder and StringBuffer in Java are objects that are designed to do string concatenation in a more efficient manner, but how much more?

We’ve got a simple Java program here that you can run from your browser so you can see it for yourself.

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In Java, an ArrayList is a very convenient object that allows us to create and manage variable-length arrays. However, in Java, an ArrayList also has a weird quirk. You cannot declare an ArrayList that uses Java primitives. Below are a few examples:

import java.util.ArrayList;

public class ArrayListTest {
	public static void main(String[] args) {
		ArrayList<int> intList = new ArrayList<int>();
		ArrayList<double> doubleList = new ArrayList<double>();
		ArrayList<char> charList = new ArrayList<char>();
	}
}

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