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![What Does It All Mean?
• public class HelloWorld {
• Declares our class/object with name “HelloWorld”. Everything inside the “{“ is part of the
class. Public is to do with it’s visibility (don’t worry about that for now).
•
public static void main(String[] args) {
• This is our “main” method, what’s called when we click “run”. The String[] args means
we can pass arguments to it, if we want to. Everything inside the “{“ is part of the main
method.
•
System.out.println("Hello World");
• This means - print out “Hello World” to the terminal. The “;” is important, it denotes the
end of the line of code. We’re going to be using a lot of these.
•
} }
• The first closing bracket denotes the end of the “main” method, the second the end of the
HelloWorld class.](https://image.slidesharecdn.com/javabuildingblocks-091117194850-phpapp02/85/Java-Building-Blocks-18-320.jpg)
![What Does It All Mean?
• public class HelloWorld {
• Declares our class/object with name “HelloWorld”. Everything inside the “{“ is part of the
class. Public is to do with it’s visibility (don’t worry about that for now).
•
public static void main(String[] args) {
• This is our “main” method, what’s called when we click “run”. The String[] args means
we can pass arguments to it, if we want to. Everything inside the “{“ is part of the main
method.
•
System.out.println("Hello World");
• This means - print out “Hello World” to the terminal. The “;” is important, it denotes the
end of the line of code. We’re going to be using a lot of these.
•
} }
• The first closing bracket denotes the end of the “main” method, the second the end of the
HelloWorld class.](https://image.slidesharecdn.com/javabuildingblocks-091117194850-phpapp02/75/Java-Building-Blocks-18-2048.jpg)
Uploaded byCate Huston
Java Building Blocks
The document serves as an introductory guide to Java, covering fundamental concepts such as object-oriented programming, the Eclipse IDE, and writing a simple 'Hello World' program. It explains primitive types, strings, conditions, and loops in Java, emphasizing how to declare variables and write clear, tidy code. Understanding these basics is essential for progressing to more complex topics in Java programming.
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Java Building Blocks
- 1. Java: Building Blocks Cate Huston @kittenthebad
- 2. What We’ll Cover • Java: an Object Oriented Language • The Eclipse IDE • Writing your first program • Primitive Types • Strings • Conditions • Loops
- 3. Java: an Object OrientedLanguage
- 4. What Does Object OrientedMean? • If Ikea were made of code, it would totally be written in an Object Oriented language. • Object-Oriented means that we break our code down into components (objects) with properties (fields), that can be used to make other objects, or interact with each other. • (See? It’s a little bit like Ikea furniture!)
- 5. OK, Give Mean Example! • Imagine a bike. If we wanted to “code” a bike, it would be a lot easier if we split it down into its component parts. • wheels (x2) • breaks • seat • frame • peddles...
- 6. Another? • How about a ToDo list? • It’s make up of tasks. • Each task should have things associated with it, such as: • It’s name • The date it’s due • The date we actually complete it • An estimate of how long it will take • The date we started it
- 7. Try It! • Thinkof a complex object • Break it down into it’s component parts • What information does each component need to know about itself?
- 8.
- 9. Eclipse is apowerful, free and open source Java IDE (Integrated Development Environment). It has some very useful features for learning to program.
- 10. Let’s start bymaking a new project. File => New => Java Project
- 11. Let’s call it“Hello World”. It’s a programming tradition.
- 12. Now we makea new “class”. Java classes are where we represent our “objects”.
- 13. Let’s call this“HelloWorld”. Notice how there are no spaces? That’s important.
- 14. Our first class! Itshould look like this.
- 15. Writing Your First Program
- 16. Finally! Write Some Code •For our first program, we’re going to write something that prints out “Hello World” in the terminal. • (Sorry, programmer tradition)
- 17. Click on “Run”(the green “play button), and see what happens.
- 18. What Does ItAll Mean? • public class HelloWorld { • Declares our class/object with name “HelloWorld”. Everything inside the “{“ is part of the class. Public is to do with it’s visibility (don’t worry about that for now). • public static void main(String[] args) { • This is our “main” method, what’s called when we click “run”. The String[] args means we can pass arguments to it, if we want to. Everything inside the “{“ is part of the main method. • System.out.println("Hello World"); • This means - print out “Hello World” to the terminal. The “;” is important, it denotes the end of the line of code. We’re going to be using a lot of these. • } } • The first closing bracket denotes the end of the “main” method, the second the end of the HelloWorld class.
- 19.
- 20. Building Blocks • Primitivesare the most basic kinds of “type” in Java (a building block!) • You can also think of them as like atoms in chemistry. • A “type” is where we say what kind of thing a variable is. • Objects are made up of other objects and primitives.
- 21. For Example... • Wholenumbers, like 42, or 926 are of type int (or short, or long). • Decimal numbers, like 2.34376 or 1.203 are float, or double. • True or False are boolean. • A character like ‘a’ or ‘c’ is a char. Notice the single quotes? Those are important.
- 22. Declaring Variables • We can declare a variable of a primitive type in Java as follows: • int i = 42; • double d = 735.27; • boolean b = true; • char c = ‘h’; • So: • type variable_name = value;
- 23. See how wecan use the “+” sign to include it in our output?
- 24.
- 25. Strings • A String is not a primitive, it’s an Object, but we can declare it like a primitive. • It’s a little more complex to declare Objects (but we’ll look at that later) • String s = “hello world”; • String s = “hello world” + “nhow are you?”
- 26.
- 27. Comparing Things • We compare things in • Equals: == Java using conditional logic. • Greater Than: > • We can put this in an “if • Less Than: < statement” • Greater Than or • if (a == b ) { ... } Equal To: >= • else if (a < b) { ... } • Less Than or Equal To: <= • else { ... }
- 28. Try this fordifferent values of a and b
- 29.
- 30. Repeating Things • Loopsare helpful for sections of code that we want to repeat. • There are three kinds of loop. • while • do while • for
- 31. For Loops • Forwhen we know how many times we want to repeat something. • 10 times • for(int i = 0; i < 10; i++) • For each character in a string • for(int i = 0; i < stringname.length(); i++)
- 32. Repeat Something 10Times
- 33. For each characterin a string. s.charAt(i) gets the character in the string at position i.
- 34. While and Do-While Loops • When we want to repeat something until a condition changes. • In a while loop we check that condition at the start of the loop • while(a == b) { ... } • In a do-while loop we check that condition at the end of the loop. • do { ... } while (a == b)
- 35.
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- 37.
- 38. Tidy Code • Tidy code is much easier to read (and debug!) • Debug - fix when it’s not working. • As a rule, indent in one inside each set of {}. • In longer sections of code, we can use // to denote a comment. • A comment is code that is ignored by the compiler. • The Java compiler ignores whitespace, so use line breaks wherever you think it will make your code clearer.
- 39.
- 40. Finally • This slidedeck covers the very basics of Java - the building blocks. • It’s important to understand these, because everything else builds upon them. • Next, we’re going to look at Processing.
- 41.