Daily Archives: November 20, 2012

Java || Snippet – How To Read & Write Data From A File

This page will consist of a demonstration of a simple quadratic formula program, which highlights the use of the input/output mechanisms of manipulating a text file. This program will read in data from a file (numbers), manipulate that data, and output new data into a different text file.

REQUIRED KNOWLEDGE FOR THIS SNIPPET

Try/Catch - What Is It?
The "Math" Class - sqrt and pow
The "Scanner" Class - Used for the input file
The "FileWriter" Class - Used for the output file
The "File" Class - Used to locate the input/output files
Working With Files

NOTE: The data file that is used in this example can be downloaded here.

In order to read in the data .txt file, you need to save the .txt file in the same directory (or folder) as your .java file is saved in. If you are using Eclipse, the default directory will probably be:


Documents > Workspace > [Your project name]

Alternatively, you can execute this command, which will give you the current directory in which your source file resides:


System.out.println(System.getProperty("user.dir"));

Whatever the case, in order to read in the data .txt file, your program must know where it is located on the system.


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output
(Remember to include the example input file)

Welcome to My Programming Notes' Java Program.

For the numbers:
a = 2.0
b = 4.0
c = -16.0

root 1 = 2.0
root 2 = -4.0

Program Success!!

Java || Snippet – How To Find The Highest & Lowest Numbers Contained In An Integer Array

This page will consist of a simple demonstration for finding the highest and lowest numbers contained in an integer array.

REQUIRED KNOWLEDGE FOR THIS SNIPPET

Integer Arrays
For Loops
Custom Setw/Setfill In Java

Finding the highest/lowest values in an array can be found in one or two ways. The first way would be via a sort, which would obviously render the highest/lowest numbers contained in the array because the values would be sorted in order from highest to lowest. But a sort may not always be practical, especially when you want to keep the array values in the same order that they originally came in.

The second method of finding the highest/lowest values is by traversing through the array, literally checking each value it contains one by one to determine if the current number which is being compared truly is a target value or not. That method will be displayed below.


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output

Welcome to My Programming Notes' Java Program.

Original array values:
36 35 46 86 86 58 44 38 79 52 27 78 65 79
------------------------------------------------------------
These are the highest and lowest array values:
Highest: 86
Lowest: 27

Java || Snippet – How To Input Numbers Into An Integer Array & Display Its Contents Back To User

This snippet demonstrates how to place numbers into an integer array. It also shows how to display the contents of the array back to the user via stdout.

REQUIRED KNOWLEDGE FOR THIS SNIPPET

Integer Arrays
For Loops
Final Variables


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output

Welcome to My Programming Notes' Java Program.

How many items do you want to place into the array?: 5

Enter item #1: 12
Enter item #2: 43
Enter item #3: 5
Enter item #4: 643
Enter item #5: 2321

The current items inside the array are:
Item #1: 12
Item #2: 43
Item #3: 5
Item #4: 643
Item #5: 2321

Java || Modulus – Celsius To Fahrenheit Conversion Displaying Degrees Divisible By 10 Using Modulus

This page will consist of two simple programs which demonstrate the use of the modulus operator (%).

REQUIRED KNOWLEDGE FOR THIS PROGRAM

Modulus
Do/While Loop
Methods (A.K.A "Functions") - What Are They?
Simple Math - Divisibility
Celsius to Fahrenheit Conversion

===== FINDING THE DIVISIBILITY OF A NUMBER =====

Take a simple arithmetic problem: what’s left over when you divide an odd number by an even number? The answer may not be easy to compute, but we know that it will most likely result in an answer which has a decimal remainder. How would we determine the divisibility of a number in a programming language like Java? That’s where the modulus operator comes in handy.

To have divisibility means that when you divide the first number by another number, the quotient (answer) is a whole number (i.e – no decimal values). Unlike the division operator, the modulus operator (‘%’), has the ability to give us the remainder of a given mathematical operation that results from performing integer division.

To illustrate this, here is a simple program which prompts the user to enter a number. Once the user enters a number, they are asked to enter in a divisor for the previous number. Using modulus, the program will determine if the second number is divisible by the first number. If the modulus result returns 0, the two numbers are divisible. If the modulus result does not return 0, the two numbers are not divisible. The program will keep re-prompting the user to enter in a correct choice until a correct result is obtained.


The above program determines if number ‘A’ is divisible be number ‘B’ via modulus. Unlike the division operator, which does not return the remainder of a number, the modulus operator does, thus we are able to find divisibility between two numbers.

To demonstrate the above code, here is a sample run:

Welcome to My Programming Notes' Java Program.

Please enter a value: 21
Please enter a factor of 21: 5

Incorrect, 21 is not divisible by 5.

Please enter a new multiple integer for 21: 7
Correct! 21 is divisible by 7

(21/7) = 3

===== CELSIUS TO FAHRENHEIT CONVERSION DISPLAYING DEGREES DIVISIBLE BY 10 =====

Now that we understand how modulus works, the second program shouldn’t be too difficult. This function first prompts the user to enter in an initial (low) value. After the program obtains the low value from the user, the program will ask for another (high) value. After it obtains the needed information, it displays all the degrees, from the range of the low number to the high number, which are divisible by 10. So if the user enters a low value of 3 and a high value of 303, the program will display all of the Celsius to Fahrenheit degrees within that range which are divisible by 10.


QUICK NOTES:
The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output

Welcome to My Programming Notes' Java Program.

Enter a low number: 3
Enter a high number: 303

Celsius Fahrenheit:
3..........37.4
10.........50
20.........68
30.........86
40........104
50........122
60........140
70........158
80........176
90........194
100.......212
110.......230
120.......248
130.......266
140.......284
150.......302
160.......320
170.......338
180.......356
190.......374
200.......392
210.......410
220.......428
230.......446
240.......464
250.......482
260.......500
270.......518
280.......536
290.......554
300.......572
303.......577.4