#Java substring how to#
#Java substring code#

In addition, this particular notation allows adjacent substrings to share a midpoint: String s = 'Luck is great, but most of life is hard work.' In particular, we get the length of the new substring: int length = endIndex - startIndex That said, there is a nice mathematical explanation for this notation, and part of it has to do with the difference between the starting and ending points. String newtonTheory = jokerQuote.substring(30, jokerQuote.length()) īut, is this really necessary? Java already provides an overload to the substring method which captures exactly this behavior. On one hand, there’s the advantage of being able to use the length of the string as the end point of the substring: String jokerQuote = 'Madness, as you know, is like gravity, all it takes is a little push.' That said, I do occasionally question the design choice. My Takeįrom what I understand, the inclusive/exclusive model is the standard for ranges in the Java API. In the next section, we’ll take a look at why that is and how I feel about it. It’s actually “Hello” because the end index is exclusive (i.e. After all, index 7 is ‘W’, the method automatically grabs the rest of the string.Īs for subTwo, we’d probably guess “Hello,”, and we’d be incorrect. Here, we can confidently predict that subOne has a value of “World!”, and we’d be right.

#Java substring code#

For example, let’s revisit some code from above: String str = 'Hello, World!' However, in practice, I find that the second option gives a lot of students trouble, and I don’t blame them.

On the other hand, we can use two indices to grab an arbitrary subset of a string. On one hand, we can use a single index to specify the starting point of our new substring. The truth of the matter is the substring method is a bit weird. We’ll need to keep this idea in the back of our mind moving forward. Once you’re done, check out the answers below: Why don’t we try a couple examples? Given “Hello, World!”, determine the substring using the following intervals: So, how does this tie into the substring method? As it turns out, a substring is a subset of a string, so we can use interval notation to define our substring. In either case, we’re describing the same set: all integers greater than 0. We could have just as easily defined the interval starting with 1-pay attention to the brackets: [1, +∞) In this example, we’ve chosen to exclude the value of 0 from the range using parentheses. In interval notation, that would look something like: (0, +∞) For instance, we may be interested in all integers greater than 0. In interval notation, the goal is to explicitly state the range of some subset. In particular, I’d like to talk a bit about interval notation. Without looking at the documentation, can you figure out what the resulting strings will be? Interval Notationīefore I give away the answer, I think it’s important to discuss some terminology from mathematics. In this example, we’ve created two new substrings: one from position 7 to the end and the other from position 0 to position 5. We need an instance of a string in order to get a substring: String str = 'Hello, World!'

In other words, subtring is an instance method which makes sense. If this is your first time poking around the Java API, this would be a good time to follow along.įirst, notice that the method header does not contain the static keyword.

#Java substring how to#

UsageĪt this point, I’d like to take a moment to show how to use the substring method. Just be aware that there are two different versions of the same method.

Java API, 2019Īt this point, don’t fixate too much on their descriptions as we’ll get to those.

Thus the length of the substring is endIndex-beginIndex. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Returns a new string that is a substring of this string. Public String substring(int beginIndex, int endIndex) The substring begins with the character at the specified index and extends to the end of this string. As a result, there are two different forms of the same method in the documentation. Well for starters, the substring method is actually an overloaded method. As you can probably imagine, it grabs a substring from a string and returns it. In this case, I’m talking about Java’s substring method. However, every once in awhile, I’ll come across a function that is less intuitive than I thought. Personally, all I need to know is the name of the command before I can figure out the rest. After all, a lot of languages support strings. But with a library so established, it sometimes feels silly to dig into the documentation. When using a library for the first time, I find it useful to check out the documentation.