Lesson01

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.