Week 1 friday
This presentation is the property of its rightful owner.
Sponsored Links
1 / 27

CS 121 PowerPoint PPT Presentation


  • 75 Views
  • Uploaded on
  • Presentation posted in: General

Week 1 - Friday. CS 121. Last time. What did we talk about last time? Our first Java program. Questions?. Java refresh. The full Hello World program Remember that everything is in a class The class name must match the file name ( Hello.java )

Download Presentation

CS 121

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Week 1 friday

Week 1 - Friday

CS 121


Last time

Last time

  • What did we talk about last time?

  • Our first Java program


Questions

Questions?


Java refresh

Java refresh

  • The full Hello World program

  • Remember that everything is in a class

  • The class name must match the file name (Hello.java)

  • The main()method is where the program starts

  • The print statement outputs information on the screen

publicclass Hello

{

  • public static void main(String[] args)

    {

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

    }

    }


More java syntax

More Java Syntax


Semicolons

Semicolons

  • In Java, like C, C++, and many other languages, we separate different statements with a semicolon ( ; )

  • If we want to do a number of statements, we just type them in order, with a semicolon after each one


Sequencing

Sequencing

  • For example, instead of one print statement, we can have several:

  • Each statement is an instruction to the computer

  • They are printed in order, one by one

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

System.out.println("Hello, galaxy!");

  • System.out.println("Goodbye, world!");


Case sensitivity

Case Sensitivity

  • Java is a case sensitive language

  • Class is not the same as class

  • System.out.println("Word!"); prints correctly

  • system.Out.Println("Word!"); does not compile


Whitespace

Whitespace

  • Java generally ignores whitespace (tabs, newlines, and spaces)

    is the same as:

  • You should use whitespace effectively to make your code readable

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

System.out.

println( "Hello, world!");


Comments

Comments

  • Programs can be confusing

  • Sometimes you want to leave notes for yourself or anyone else who is reading your code

  • The standard way to do this is by using comments

  • Although comments appear in the code, they do not affect the final program


Comments1

Comments

  • There are two kinds of comments (actually 3)

  • Single line comments use //

  • Multi-line comments start with a /* and end with a */

System.out.println("Hi!"); // this is a comment

System.out.println("Hi!"); /* this is

a multi-line

comment */


What we know

What we know

  • Java is a large, complex language

  • Even so, there are only a few tasks that you can ask it to do

  • You have already learned:

    • Sequencing

    • Basic output


Where we are headed

Where we are headed

  • There are not that many other things you can tell Java to do

    • Storing numbers and text

    • Basic mathematical operations

    • Choosing between several options

    • Doing a task repetitively

    • Storing lists of things

    • More complicated input and output

    • Naming a task so that you can use it over and over again

  • That’s basically it


Software development

Software Development


What is programming again

What is programming again?

  • The process of giving computers very detailed instructions about what to do

  • How do we do that exactly?

  • First, we need a programming language like Java

  • How do we turn a set of instructions written so that a human can read them into a set of instructions that a computer can read?

  • Magic, of course!


First let s talk about languages

First, let’s talk about languages

  • There are many different programming languages:

    • Java

    • C/C++

    • ML

    • …thousands more

  • Each has different advantages in different situations


High vs low

High vs. low

  • We classify languages as high or low level

  • High level languages allow you to give more abstract commands that are more like human thought processes or mathematics

  • Low level languages are closer to the computer world and give explicit instructions for the hardware to follow

Low

High


Compilers

Compilers

  • We use a program called a compiler to turn a high level language into a low level language

  • Usually, the low level language is machine code

  • With, Java it's a little more complex


How does that work in general

How does that work in general?

Source Code

Machine Code

Hardware


What s the issue with java

What’s the issue with Java?

  • Java is a more complicated

  • Java runs on a virtual machine, called the JVM

  • Java is compiled to an intermediate stage called bytecode, which is platform independent

  • Then, the JVM runs a just-in-time compiler whenever you run a Java program, to turn the bytecode into platform dependent machine code


Compilation and execution for java

Compilation and execution for Java

Java

Source

Code

Machine Code

Java Bytecode

Hardware

Platform

Independent

Platform

Dependent


Let s review the steps we ll use

Let’s review the steps we’ll use

  • Write a program in Java

  • Compile the program into bytecode

  • Run the bytecode using the JVM (which automatically compiles the bytecode to machine code)


Software development1

Software development

Often goes through phases similar to the following:

  • Understand the problem

  • Plan a solution to the problem

  • Implement the solution in a programming language

  • Test the solution

  • Maintain the solution and do bug fixes

    Factor of 10 rule!


Lab 1

Lab 1


Upcoming

Upcoming


Next time

Next time…

  • We'll talk about data representation


Reminders

Reminders

  • Reading Chapter 3

  • Look at Project 1

  • No class on Monday!


  • Login