97 Things Every Java Programmer Should Know

Chapter 50. Learn Java Idioms and Cache in Your Brain

Jeanne Boyarsky

As programmers, there are some tasks we need to do frequently. For example, going through data and applying a condition are common. Here are two ways to count how many positive numbers are in a list:

public int loopImplementation(int[] nums) {
  int count = 0;
  for (int num : nums) {
    if (num > 0) {
      count++;
    }
  }
  return count;
}

public long streamImplementation(int[] nums) {
  return Arrays.stream(nums)
               .filter(n -> n > 0)
               .count();
}

Both of these accomplish the same thing, and they both use common Java idioms. An idiom is a common way of expressing some small piece of functionality that the community has general agreement on. Knowing how to write these quickly without having to think about them enables you to write code much faster. As you write code, look for patterns like these. You can even practice them to get faster and learn them by heart.

Some idioms, like looping, conditions, and streams, apply to all Java programmers. Others are more specific to the types of code you work on. For example, I do a lot with regular expressions and file I/O. The following idiom is one I commonly use in file I/O. It reads a file, removes any blank lines, and writes it back:

Path path = Paths.get("words.txt");
List<String> lines = Files.readAllLines(path);
lines.removeIf(t -> t.trim().isEmpty());
Files.write(path, lines);