Java Tutorial - Basic data types and variables

In computer science, data is information that is stored or processed by a computer. While that might seem fairly abstract, there are many data points we use in everyday life. Your name, your age, the number of apples in your pantry, whether your kitchen light is on or off, these can all be considered pieces of data. And we represent pieces of data in code using data types. Similar to other programming languages, Java classifies different pieces of data with data types based on their value. For example, there's a data type for letters and symbols, and there are various data types for numbers. Ultimately, a data type provides a set of possible values. And if a piece of data is one of these values, it is classified as that specific type. Java separates its data types into two main categories. One of the categories is called primitive data types, which consist of the most basic data types in the Java language. These are the most foundational. The Boolean data type represents a true or false value. This means the data piece of whether the kitchen light is on or off could be represented as a Boolean in code. It might have the value true, or it might have the value false, but it can never be both. An int, short for integer, represents a whole number. The number of siblings you have could be represented in code as an int. You could have zero siblings, three siblings, 10 siblings, any whole number amount of siblings. A double represents a decimal number. With a double, you can represent your GPA, say 3.4, in Java. The last primitive type is a char, which is short for character. A char represents a single letter or symbol. Some possible values for a char could be your first initial or last initial, your favorite letter, or the hashtag symbol. We classify these data types as primitive types because they are the basis and foundation for all other data types within the Java programming language. Let's try using our primitive types in Java. We'll be creating a few pieces of data that could represent attributes of a given high school student. We could represent a student's age by just writing 15. Then we could represent a student's GPA with just 3.45. However, we get errors. What we've written are technically numbers and pieces of data, but in Java, we save data in something called a variable. A variable is a way to label data and reference it later in your program. Instead of saying 15, we can create a label, say student age, and then assign a value to it, in this case, 15. We still get an error here, and that's because we need to add a data type to the variable. We can add int at the beginning of the line and then a semicolon at the end of the line to end the statement, and all of our errors are gone. As you can see, a variable has a data type, label, and value. In this case, the data type is int. The label is student age, and the value is 15. The equal sign is an assignment operator that assigns the int variable with the label student age and the value 15. Let's create the next piece of data in Java, a student's GPA. We need to create another variable, and we decided before that that data type would be double. So let's write double and give the variable the label student GPA, and then we'll sign it the value 3.45 and add a semicolon to end the statement. Next, we'll represent a student's first initial with the data type char student first initial as the label and give it the value K. We'll do something similar for the student's last initial with the data type char label student last initial and give it the value H. For all of these variables, you could put a different value as long as it can still be represented by that given data type. For example, you couldn't put a letter or symbol as the value of student age, but you could put another whole number, say 17 instead of 15. The last piece of data we want to represent is has perfect attendance. Like the other variables, we'll write the data type Boolean, the label has perfect attendance, and then give it the value true. You may notice that our variable names are grayed out. That's because although we've created a piece of data and represented it in Java, we don't use or reference it in our program. One way we could reference it is by printing out the value of the variable to the console. We'll write system.out.println, and instead of adding quotes, we'll just write the name of the variable. Since student age has the value 15, we'll print out 15 to the console. We'll save this and then click the play button, or you could left click and hit run main.main, and we get 15 in our console. Let's try this with the other variables. We'll write system.out.println, student GPA, system.out.println, student first initial, system.out.println, the last initial, and then the has perfect attendance. We'll run this again, and we get 15, 3.45, K, H, and true, as expected in the console.