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.

/* 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.")
        //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:

a number is divided by zero.

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

            int result = 2 / 0;
            System.out.println("Result: " + result);
        } catch (ArithmeticException e) {  //this just makes the error more verbose
            e.printStackTrace();
        }
    }
}
exceptionError.main(null)

java.lang.ArithmeticException: / by zero
	at REPL.$JShell$20$exceptionError.main($JShell$20.java:19)
	at REPL.$JShell$21.do_it$($JShell$21.java:16)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:578)
	at io.github.spencerpark.ijava.execution.IJavaExecutionControl.lambda$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



_3_ False

_4_ "ryan gosling"

_1_ 1738

_2_ 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 private;

integer sum;

double wow!;

boolean foundIt;

int numberOfStudents;

double chanceOfRain;

boolean #mortNews;

int count;

bool isFriday;

final int DOZEN;

1.3 Main Topics

Literal vs String Literal

Arithmetic operators

Additon
Minus
Multiply
Divide
Mod

Arthemtic expressions

Int
Double

Assigment Operator

= vs ==

Demo 1

public class demo {
    public static void main(String[] args) {
        // Whats is the outputs between these two pieces of code
        //
        //
        //
        
        
        System.out.println("3" + "3");
        System.out.println(3 / 2);
        System.out.println(2.0 * 1.5);
        
    }
}

demo.main(null);

33
1
3.0

Cheat Sheet

Literal

The source code representation of a fixed value

String Literal

Something enclosed in double qoutes

Assigment Operator

= is an assigment operator
== is repesents just normal =
Assigment Operators moves right to left
X = Y = Z = 2;
Why is 7 = x; a non valid peice of code

PEMDAS

Java uses PEMDAS still but a tiny bit different

Order

()
*, /, %
+, -

Primative Data Types

table

Operation vs Result

The bigger data type will always be the resulting output
If you were to add a double and a int what would be the result?

Demo 2

public class demo2 {
    public static void main(String[] args) {
        // Print a math equation that goes through these steps
        // Adds 19 + 134
        // Multiplies that value by 5
        // Then takes the mod of that value by 2
        // It should print 1

        System.out.println( (19 + 134) * 5 % 2);
    }
}

demo2.main(null);

Odd Even

public class OddEven {

    // Without changing any varibles
    // Print only odd numbers

    public static void main(String[] args) {
        int num = 2;
        int i = 0;
        while (i <= 10) {
            if (i % num == 1) {
                System.out.println(i + " is odd");
            }
            i++;
        }
    }
}

OddEven.main(null);

is odd
is odd
is odd
is odd
is odd

1.4 Compound Assignment Operators

look at storing items in variables with assignment statemt.

also look at compound assignment operators (+=, -= etc) to modify values stored in variables in one step

+= adds value to existing variable value

x += 7 is equivalent to x = x + 7; x -= 5 is equivalent to x = x - 5;

same for all compound assignment operators.

also learn how to trace through code (check comments of codeblock below)

public class CompoundDemo {
    public static void main(String[] args) {
        int x = 6;
        x += 7; // 6 + 7 = 13
        x -= 3; // 13 - 3 = 10
        System.out.println(x);
        x *= 10; // 10 * 10
        x /= 5; // 100 / 5 = 20
        System.out.println(x);
        x %= 3; // remainder of 100/3 = 2
        System.out.println(x);
}
}
CompoundDemo.main(null);

// NOTE: going through these compound assignments with comments is called tracing,
// when we do what the compiler does, and go through the code step by step. Should be
//done on the AP test to avoid human error.

10
20
2

increment and decrement operator

IMPORTANT: THE USE OF INCREMENT AND DECREMENT OPERATORS IN THE PREFIX FORM (++X) AND INSIDE OTHER EXPRESSIONS (ARR[X++]) IS OUTSIDE THE SCOPE OF THE COURSE AND THE AP EXAM

public class incdecDemo {
    public static void main(String[] args) {
    int x = 1; 
    int y = 1;
    x++; // x = x + 1, x = 2;
    y--; // y = y - 1, y = 1 - 1 = 1;
    System.out.println(x);
    System.out.println(y);
}
}
incdecDemo.main(null);

// NOTE: going through these compound assignments in order is important to
// ensure you get the correct output at the end

2
0

learn how to describe code

the following code segment has comments that describe the line of code the comment is on. Look at how the code is described.

public class behaviorDemo {
    public static void main(String[] args) {
    int x = 20; // define an int variable x and set its initial value to 23
    x *= 2; // take the current value of x, multiply it by 2, assign the result back to x
    x %= 10; // take the current value of x, find x modulus 10 (remainder x divided by 10), 
    //assign result back to x
    System.out.println(x); // display the current value of x
}
}
behaviorDemo.main(null);

practice important concepts

public class numbers {
    public static void main(String[] args) {
        int x = 777;

        // challenge: think of 2 compound assignment operators that can be used in tandem to get the following outputs
        // example: if we wanted output of 1 with 2 compound assigment operators, using x++; and x /= 777 would work. now how would we do that for:
        
        // 100?

        // 779?

        // 2?

        System.out.println(x);
}
}
CompoundDemo.main(null);

10
20
2

// PRACTICE TRACING THROUGH THE FOLLOWING CODE (someone could come up and do it on a whiteboard if we have time for fun)

public class Demo {
    public static void main(String[] args) {
        int x = 758;
        x += 423; 
        x -= 137; 
        x *= 99; 
        x /= 33; 
        x %= 111; 
        System.out.println(x);
}
}
CompoundDemo.main(null);

10
20
2

// DESCRIBE EACH LINE OF CODE
int x = 5; 
x++;
x /= 2;
System.out.println(x);

what you must know

compound operators perform an operation on a variable and assign the result to the variable

ex: x /= 25; would take x and divide it by 25, then assign the result to x.

if x = 100, then the result of x/= 25; would be 4.

increment and decrement operators take x and either increment it or decrement it by 1, then assign the value to x.

x++; would take x and add 1 to it, then assign the value to x.

x–; takes x and subtracts 1 from x, then assigns the value to x.

your frq will likely see if you know how to use compound operators in actual code.

mini hacks:

write some java code that uses compound operators and then trace through it similarly to the examples shown in this lesson. Use conditional statements as well, don’t just execute some compound operators on an x value in order and call it a day. You might have to do tracing on the AP test so this is for your own good.

example below

public class CompoundAssignment {

    public static void main(String[] args) {
      
      int sum = 0; 
      for (int i = 0; i < 2; i++) {  // i = i + 1 each iteration, 1st iteration i = 0
        for (int j = 0; j < 2; j++) { // j = j + 1 each iteration, 1st iteration j = 0
          System.out.println("i: " + i);
          System.out.println("j: " + j);
          sum += i + j; //  sum = sum + (i + j) each iteration, 1st iteration sum = 0 + (0 + 0)
          System.out.println(sum);

        }
      }
      
      System.out.println("Sum: " + sum);
  
  } }
CompoundAssignment.main(null);

1.5

Casting Variable

CASTING

"Change the data type of variable from one type to another."

Example

Int variable —-» double
String variable —-» Int

/*
* Purpose: Demonstrate casting using division.
*/
public class CastingNumbers {
    public static void main(String[] args) {
        System.out.println(6 / 4); // if I just do divide 6 by 4, these are both int value, so I'm going to wing up with an int result.
        System.out.println (6.0 / 4); // Since one of those value is a double value, output will be double 
        System.out.println(6 / 4.0); // (Same Reason) I wind up with the result of 1.5
    }
}

Ranges of variable

int: Stored by using a finite amount (4 bytes) of memory.

Integer

Max: 2,147,483,647
Min: -2,147,483,648

Double

up to 14 - 15 digits for storage

Boolean

only 2 (true and false)

/*
* Purpose: Demonstrate Integer Range
*/
public class TooBigNumber {
    public static void main(String[] args) {
        int posInt = 2147483647; 
        int negInt = -2147483648;
        System.out.println(posInt + " "); 
        System.out.println(negInt);
    }
}
TooBigNumber.main(null);

2147483647 
-2147483648

/*
* Purpose: Demonstrate Integer.MAX_VALUE and Integer.MIN_VALUE.
*/
public class IntMinMax {
    public static void main(String[] args) {
        int posInt = Integer.MAX_VALUE; 
        int negInt = Integer.MIN_VALUE;
        System.out.println(posInt + " "); 
        System.out.println(negInt);
    }
}
IntMinMax.main(null);

2147483647 
-2147483648

/*
* Purpose: Demonstrate Integer Overflow
*/
public class TooBigNumber {
    public static void main(String[] args) {
        int posInt = Integer.MAX_VALUE; 
        int negInt = Integer.MIN_VALUE;
        System.out.println(posInt + 1); 
        System.out.println(negInt - 1);
    }
}
TooBigNumber.main(null);

-2147483648
2147483647

import java.util.Scanner;

public class Sum_forABC {
	public static void main(String args[]) {
		int a = 70;
		int b = 63;
		int c = 82;
		
		int total = a + b + c;
        
		double avg = total / 3; 
		
		System.out.println("a\tb\tc");
		System.out.println(a+"\t"+b+"\t"+c);
		System.out.println("total:" + total);
		System.out.printf("average: %.2f", avg);
	}
}
Sum_forABC.main(null);

a	b	c
70	63	82
total:215
average: 71.00

<!DOCTYPE html>

Java Code Runner

Questions

1. what will be the output of (int) (2.5 * 3.0)

2. what will be the output of (double) 25 / 4

3. what will be the output of 6 / (double) 5

4. what will be the output of (int) (-8.63 - 0.5)

Essential Knowledge (2.B)

The casting operators (int) and (double) can be used to created temporary value converted into a different data type.
Casting a double value to an int causes the digits to the right of the decimal point to be truncated.
Some programming code causes int values to be automatically cast(widened) to double values.
Value of type double can be rounded to the nearest integer (int) (x + 0.5) + (int) (x - 0.5) for negative numbers.

Essential Knowledge (5.B)

Integer values in Java are represented by values of type int, which are stored using a finite amount (4 bytes) of memory. Therefore, an int value must be in the range from Integer.MIN_VALUE to Integer.MAX_VALUE inclusive.
If an expression would evaluate to an int value outside of the allowed range, an integer overflow occurs. This could result in an incorrect value within the allowed range.

Questions

(int) (2.5 * 3.0)
(double) 25 / 4
6 / (double) 5

Mini Hacks

Complete all uncompleted code segments
Answer all questions in the code
complete the activities in the lesson blogs
will be scaled to 0.2 depending on the completion of your code

Main Hack

Use topics from 3 out of 4 of the Units
It has to be a 2 part style question, A and B
Will Be graded out of 4 points
Write a scoring sheet for what you have done out six points
Your real grade for the assigment will be based of two things
How creative, unique, cool your question and code is
Did you acheive 4/4 points for your code
That will be scaled to 0.8 of 1 for all your hacks

Answer to Hacks (1999 #3)

3.a

Write a new BigInt member function Div2, as started below. Div2 should change the value of the BigInt to be the original value divided by 2 (integer division). Assume the BigInt is greater than or equal to 0. One algorithm for implementing Div2 is:

Initialize a variable carryDown to 0.
For each digit, d, starting with the most significant digit,
1 replace that digit with (d/2) + carryDown
2 let carryDown be (d%2) * 5
Normalize the result

Complete member functionDiv2 below

void BigInt::Div2()
// precondition: BigInt >= 0

void BigInt::Div2(){
    int carrDown = 0
    int d;

    for(int i = myNumDigits - 1, i >= 0, i--){
        d = GetDigit(i);
        changeDigit(i, (d/2) = carryDown);
        carryDown = (d % 2) * 5;
    }
    Normalize();
}

3.b

Initialize low to 0 and high to dividend.
For each iteration, 
1 compute mid = (low + high + 1)
2 divide mid by 2
3 if mid * divisor is larger than dividend (mid is too large to be the quotient) then set high equal to mid - 1 else set low equal to mid.
when low == high the search terminates, and you should return low.

BigInt operator/ (const BigInt & dividend, const BigInt & divisor){
    BigInt low(0), high(dividend), mid;
    while(low != high)
    {
        mid = (low + high + 1);
        mid.Div2();
        if (mid * divisor > dividend){
            high = mid - 1;
        }
        else{
            low = mid;
        }
    }
    return low;
}