SECTION 1.1

Why does java matter?

one of the main reason that java is such an important language in the coding world is because it is a object-oriented-programming (OOP) language.

it offers a structure that is easy to solve big problems. but i think that we all know that so lets skip to the real deal.

Basics of Java

Block Comments- The compiler will ignore any text between /* and */
line comments- Same as above but // ignores one line
Class Declaration - identifies the name, the start and the end of the class. the class name must match the file name. (case sensitive)
main Method- controls all of the action in the program.
system.out- objects that generate output to the console
system.out.print- prints what ever you out inside the ()
system.out.println- prints whatever is one the screen and moves to the next line to print out the next action. basically hits enter after it prints out.

tip: add “<classname>.main(null)” at the end of your code to see the output in your jupyter notebook.

Example:

/* this is a
   code block */


// code: printing out hello world. 

public class greeting {
    public static void main (String [] args) {

        System.out.println("Hello, World!");
        System.out.print("Hello,");
        System.out.print(" World!"); 
    }
}

greeting.main(null)

Hello, World!
Hello, World!

What is a string literal?

any sequence of letters, numbers, or symbols that is put between quotes.
java will put out anything in the quotes, no restrictions.

Examples:

public class stingLiterals {
    public static void main (String [] args) {

        System.out.println("This is a string literal.");
        System.out.println("and so are these");
        System.out.println("1234567890"); 
        System.out.println("&^&*%^$&%$#^%W#*^$%&(*^)"); 
    }
}

stingLiterals.main(null)

This is a string literal.
and so are these
1234567890
&^&*%^$&%$#^%W#*^$%&(*^)

ERRORS!!!!!!

Syntax/compiler error:

messed up syntax
compiler is not happy >:(

public class syntaxError {
    public static void main (String [] args) {

        system.out.println("This is a syntax error.")
        //uncapitalized s
        //missing semicolon
    }
}

syntaxError.main(null)

|           system.out.println("This is a syntax error.")

';' expected

Logic Error

compiler is happy
messed up in the string literals
code works perfectly

public class logicError {
    public static void main (String [] args) {

        System.out.println("This is a leogic error.");

    }
}

logicError.main(null)

This is a leogic error.

exception error:

public class exceptionError {
    public static void main(String[] args) {
        try {

            int result = 2 / 0;
            System.out.println("Result: " + result);
        } catch (ArithmeticException e) {  
            e.printStackTrace();
        }
    }
}
exceptionError.main(null)

java.lang.ArithmeticException: / by zero
	at REPL.$JShell$42C$exceptionError.main($JShell$42C.java:19)
	at REPL.$JShell$45.do_it$($JShell$45.java:16)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:578)
	at io.github.spencerpark.ijava.execution.IJavaExecutionControl.lambda$execute$1(IJavaExecutionControl.java:95)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
	at java.base/java.lang.Thread.run(Thread.java:1623)

SECTION 1.2

Variable and Data Types.

Primitive Data

determines the size and type of data can we can worth with in a java program.
focus on three different types that can we can represent data.

Smallest to biggest:

Boolean, takes up 1 bit.

true or false

Int, take up 32 bit

whole number values.
add, subtract, multiply, etc.

Doubles, AKA Floating point numbers. 64 bit

same as integers

String

“Hello World!”

Reference Purposes

(the collegeboard person used bows as reference so will i.)

there can be small bow
a medium bow
a red bow
a large red bow

What is the difference?

primitive data are already in java, you don’t have to make it. Except for string, which is created by the programmer.
non-primitive data can be use methods to perform actions, but primitive data cannot.

Primitive Activity

MIX&MATCH

Choices:
1. int
2. double
3. boolean
4. String



__ False

__ "ryan gosling"

__ 1738

__ 4.26

Questions:

what type of data should be used to store

someones bank number and cvc?
someones mother’s maiden name and their name?
the first 16 digits of pi
if you want to transact one million $.

Variables

A name given to a memory location that is holding a specified type of value.

how to name a variable (omg this is so hard !)

may consists of letters, digits, or an underscore (case sensitive)
may not start with a digit
space are a big no no
may not use other characters as &,@, or #
may not used java reserved words

Tip!

use camel casing when naming a variables.

example:

thisIsCamelCasing

Declare variables:

The three primitiva data types in Java:

integers (whole #): int
Decimal numbers (floating-point values): double
Boolean values (true/false): boolean

Format:

dataType varibleName;

Example

int total;

boolean outcome;

double firstFifteenPi;

what if you don’t want to change the variable’s value after given?

add final in front of the declaration:

final double PI;

final boolean WORKOUT_DECISION;

for final variables, use all caps and underscore when naming them.

Practice

Find the odd one out.

int value;

double 4eva;

boolean public;

integer sum;

double wow!;

boolean foundIt;

int numberOfPigs;

double chanceOfRain;

boolean #apDaily;

int count;

bool isFriday;

final int DOZEN;

Section 1.1 and 1.2 • 13 min read

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