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Lesson One

Table of Contents

The Lesson
The Program

The Lesson

  • In this lesson you can see the basics of Java at work:
  • Variables:
    • Variables can be set equal to either literals, objects, or other variables.
      • String name = "Hi";
      • String name = new String();
      • String name = otherString; (Other string is a variable that we are pretending exists)
    • As you can see, variables are created (declared) by stating the type (String in this case) and then the name (name).
      • Other types include int, long, char, boolean, double, and float.
        • These are called the primitive types.
        • You can also use Classes as types but we will deal with that later just don't be surprised when you see it.
      • You then set variables using a single = sign and then on the right you put what you are setting it to.
        • Setting is also called initialization if you are doing it to a variable for the first time.
    • Examples of variables in this lesson include name, age, and favoriteLetter.
  • Literals:
    • Literals are things that are hard coded into your java code and computer.
    • Literals come in pretty much every form for all of the primitives as well as for Strings.
      • Primitives = int, long, char, boolean, double, float
        • All primitives are colored purple in Java.
          • Keywords and other things are also colored purple so make sure not to get confused.
      • Literal Forms of primitives = int literal (1), char literal ('c'), boolean literal (true), etc.
      • String literals ("hi") also exist but String is not a primitive. * You may notice how String is not purple in our code. It's not a primitive but a class which we'll talk about later.
    • Examples of literals in this lesson include "Carl", 5, and 'c'.
  • Objects:
    • Objects are things that we will talk about later but for now you just need to know that they are instances of classes.
    • There are no concrete examples of objects in this lesson.
  • System.out:
    • System is a class that contains a variable named out.
    • The variable out holds an object that has many functions but the three that we care about are:
      • print(String x) - Let's you print simple text to the console.
        • In order to print a new line you should use "\n".
      • println(String x) - Let's you print simple text to the console and then move to the next line.
      • printf(String x, String y, String z, ...) - Let's you print formatted text to the console.
        • The ... is me saying that there can be an unlimited amount of Strings passed into the method.
          • We will talk about methods in more depth later so don't worry about it this too much just know how to do it.
          • Also keep in mind that you can pass in primitives to this method as they will be treated as Strings.
        • Inside your first string (x) you have to use %s or %d to denote where your other strings should be put.
          • %s is for Strings
          • %d is for numbers although %s will still work for primitive numbers since they are treated like strings.
    • The + Math operator can be used to combine two strings or a string and a primitive so you can emulate how printf works.

The Program

  • In the program we assign create three variables (name, age, and favoriteLetter) and assign them to the appropriate literals.
  • We then mess around with printing some text to the console including through the use of these variables.