Data Types#
Note
Above, you’ll see there’s a video titled CSE 121: Data Types Video Walkthrough.The video and the reading both have the same information. You’re not required to go through both the video and the reading, as the video just walks through the reading to help contextualize it!
Aside from displaying text to the console, one of the most important needs for a programmer is the ability to store information. Whether it’s storing the name of a user, the balance of a bank account, or the current year, it is very useful to be able to give information a label, and reference it. We can do this in Java using variables (more on variables in the next lesson).
🧠 Data Types#
When deciding what information to store, you first need to decide what type of data it should be so that Java can be prepared for what you want to give it. This could be something like a number, word, or letter! Java has formal names for each of these types.
Note
We’ll see examples on how to use these data types in the next section!
Integers#
Integers are whole numbers such as 1, 2, 3, 0, -1, -50, etc. We can tell Java that we want to store an integer using the int keyword. Integers are useful for representing quantities like the number of people in a room, your age, or other discrete (whole number) quantities.
Caution
✅ Valid Integers: 121, 2022, 10, 75
❌ Not Valid Integers: 3.14, 0.5, “Hello”, “10000” (even though the last example is an integer, note it has quotes!)
Doubles#
Doubles are decimal numbers such as 0.25, -3.56, 3.14, 500.0, etc. We can tell Java that we want to store a decimal number using the double keyword. Doubles are useful for representing quantities like money (dollars and cents), weight, and so on. Doubles are typically used in situations where we need more precision than simple integers (whole numbers).
Caution
✅ Valid Doubles: 9.81, 98.6, 1.0,10.5772984
❌ Not Valid Doubles: “Hello”, “10.5” (even though the last example is a double, note it has quotes!)
Strings#
Strings represent text such as “Hello”, “Bye”, “CSE 121”, etc. You can think of strings as a collection of letters, digits, or other characters that are strung together to form a word or a sentence. We can tell Java that we want to store text using the String keyword (notice the capital S), typically with double quotes around the text.
Caution
✅ Valid Strings: “java-!”, “a longer string”
❌ Not Valid Strings: 10000 (notice no quotes)
Booleans#
A boolean is a data type that has only two possible values: true or false. Booleans are intended to represent the output of a logical calculation. We can tell Java that we want to store a true/false value using the boolean keyword. You probably won’t use boolean values much for now, but as we continue to build on our Java knowledge, they will indeed become more useful!
Caution
✅ Valid Booleans: true, false (these are the only two values that a boolean can be)
❌ Not Valid Booleans: “true”, “false”, 10, 100.5, “hi”
Main Points#
We’ve learned about 4 data types in Java: integers (
int) which represent whole numbers, doubles (double) which represent real numbers, strings (String) which represent text or a sequence of characters, and booleans (boolean) which represent truth value (i.e.,trueorfalse).