Lecture Code #

Code from this lecture available at https://github.com/Berkeley-CS61B/lectureCode-sp23/tree/main/lec1_intro1.

Overview #

Our First Java Program. Printing Hello World looks like this:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello world!");
    }
}

Key Syntax Features. Our first programs reveal several important syntax features of Java:

• Curly braces are used to denote the beginning and end of a section of code, e.g. a class or method declaration.
• All code lives inside a class.

  public class HelloWorld {
   // everything between these two curly braces is within this class!
  }
  

• The code that is executed when a program starts is inside a function, a.k.a. method, called main.

  public static void main(String[] args) {
   //The body of this method is what is executed
  }
  

• Statements end with semi-colons;

System.out.println("Hello world!");

• Variables have declared types, also called their “static type” and variables must be declared before use.

   String greeting = "Hello World";
  

• Functions must have a return type. Return types must be specified in the method signature. If a function does not return anything, we use void to specify this.

  public static void main(String[] args) {
   //This method does not return anything, so we use void
  }
  

• The compiler ensures type consistency. If types are inconsistent, the program will not compile.

Static Typing. Every variable, parameter, and function has a declared type, making it easier for a programmer to understand and reason about code. This is known as static typing.

• Static typing is (in my opinion) one of the best features of Java. It gives us a number of important advantages over languages without static typing.
• Types are checked before the program is even run, allowing developers to catch type errors with ease.
• If you write a program and distribute the compiled version, it is (mostly) guaranteed to be free of any type errors. This makes your code more reliable.

There are downside of static typing, to be discussed later.

Exercises #

Today’s guide only provides check-in questions, which are linked here

However, we strongly encourage you to complete the optional HW0, which covers a bunch of basic Java syntax.