Java string substring how to#
Java string substring code#

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 string 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.

Java string substring code#

The following code is simplified and only contains the key point for explain this problem.When using a library for the first time, I find it useful to check out the documentation. The difference between the two Strings is their count and offset values. When the substring() method is called, it creates a new string, but the string's value still points to the same array in the heap. They are used to store real character array, the first index of the array, the number of characters in the String. In JDK 6, the String class contains 3 fields: char value, int offset, int count. String is supported by a char array in the back-end. What exactly happens when substring() is called is different between JDK 6 and JDK 7. However, this diagram is not exactly right. You may know that because x is immutable, when x is assigned with the result of x.substring(1,3), it points to a new string like the following: