$/*$ APCSA Ch $85$ex$99$: ArrayList of Integer objects STU

by Burkham, v$\mathrm{.}8$a $29$jan$24(7$feb$23,16$feb$22,20$jan$22,15$feb$21)$

REQUIRED:

You must be fluent with everything in this program for the AP exam.

Examine and study each method carefully!

WRITE $3$ METHODS:

$1.$ sumArrayList$()$

This method must return int, which is the sum each int in $1-$D array.

You must use a 'normal' for loop $($counting loop$).$

Use a wrapper Integer with number at each index.

It should take about $6$ lines of code, at most.

$2.$ sumArrayListEnhancedForLoop$()$

This method returns an int by summing each int in $1-$D array, using

and 'enhanced' for loop, not a counting loop.

Cast from Integers with $($int$).$

It should take about $3$ lines of code, at most.

$3.$ pctNegNumbers$()$

This method returns an int, the percent negative numbers $($rounded$)$ in array.

Use an Enhanced For Loop $($not a counting loop!$).$

Round the result to an integer $($no decimal places$),$ using $($int$)$ cast

of a double.

This program demonstrates:

ARRAYLIST

$-$ how values stored into an object

$-$ how objects must first convert to objects

$-$ ArrayList return

$-$ ArrayList $.$add$()$ method

$-$ use of ArrayList $.$size$()$ method

STRING

$-$ use of String $.$length$()$ method

$-$ String concatenation

$-$ complex String building

$-$ use of both $.$substring$()$ method contexts $($overloads$)$

$-$ creation and use of literal String object inside $(),$ then calling methods

WRAPPER

$-$ how the class $($called a "wrapper" class$)$ is used

LOOPING

$-$ Standard & Enhanced

CLASSES

$-$ Class used only for doing things $($methods$),$ 'static'

$-$ No instance anything

$-$ Pure Static: No Constructor, No PIV, No V$,$ only static methods

METHODS

$-$ how static methods are used

$-$ how static methods are called from another class

$-$ void return

$-$ int return

MATH & OTHER

$-$ modulo division to print variable quantities of numbers per line

$-$ use of Math.random$()$ to create three digit integers

$-$ use of $+=,$ &&$,==,!=$

$-$ print formatting $($fixed length strings for columns of numbers$)$

$-$ use of tab, $"\backslash$t$"$

$-$ use of new line, $"$

$"$

TOM CLASS

$-$ STATIC METHODS used:

$--$ createArrayListOfIntegers$($int$,$int$)-->$ Returns a $1-$D ArrayList, containing int objects

$--$ printArrayList$($int$,$int$)-->$ Prints; Returns nothing

$--$ sumArrayList$($ArrayList$)-->$ Returns int: the sum of all array numbers

$--$ sumArrayListEnhancedForLoop$($ArrayList$)-->$ Returns int: sum of all array numbers

$--$ pctNegNumbers$($ArrayList$)-->$ Return percent of negative number in $1-$D array

SAMPLE OUTPUT $($for $50$ numbers, $10$ per line$)$:

$1-$D Array of $50$ numbers, formatted in $10$ columns:

$12345678910$

$|--------------------------------------------------$

$1|-714232-539246805-710-193519411-728$

$11|-45-162859664314-73921-436234988$

$21|93710-877-332306972-453-134604246$

$31|302700-963-577462175111724-562764$

$41|-613-482-253218-791611580-237-758-460$

Sum of $50$ numbers using Normal 'for' Loop: $1113$

Sum of $50$ numbers using Enhanced 'for' Loop: $1113$

$50\%$ DESIRED Neg Numbers

$46\%$ ACTUAL Neg Numbers

$*/$

import java.util.ArrayList;

$//========================================================================================$

$//======$ This runner class contains the main method to actually run the program $========$

$//========================================================================================$

public class Ch$85\_$ArrayList$\_$IntegerObjects$\_$STU$8$a $\{//$ Runner class

public static void main$($String$[]$ args$)\{//----$ BEGIN JAVA PROGRAM $----$

int numNums $=50$; $//$ choose how many numbers to create

int numPctNeg $=50$; $//$ target $\%$ neg numbers to have $(00-100)//$#

int numsPerLine $=10$; $//$ how many numbers to print per line

$//$# SOURCE OF: warning: $[$unchecked$]$ unchecked conversion

$//$# Because ArrayList was created in a class's method, and returned as reference $($warnings are OK$!)$

$//$# Java 'thinks' $($correctly$)$ it $*$could$*$ cause an error in $*$other$*$ circumstances, such as using

$//$# Double instead of Integer in the called method createArrayListOfIntegers$()$

ArrayList numbers $=$ Tom.createArrayListOfIntegers$($numNums$,$numPctNeg$)$; $//$#

Tom.printArrayList$($numbers$,$numsPerLine$)$; $//$ print $1-$D array in chosen format $($# per line$)$

System.out.println$("$

Sum of $"+$numNums$+"$ numbers using Normal 'for' Loop: $"$

$+$Tom.sumArrayList$($numbers$))$; $//$ sum with normal for loop

System.out.println$("$Sum of $"+$numNums$+"$ numbers using Enhanced 'for' Loo