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Enhanced For Statement - JavaDevelopmentForums.com

OA-OD-JD1 — Sun, 29 Jan 2012 22:08:01 GMT

When working with arrays, there's an easier way to loop through the indices than manually doing so. We can use the enhanced for statement for this.
class Class1{
   public static void main(String args[]){
	   int aryOne[] = {3,4,5,6,7};
	   int total = 0;
	   for (int x: aryOne){
		   total += x;
	   }
	   System.out.println(total);
   }
}
First of all, we create our array (aryOne) and use an array initialiser to give it some values. We then create a total variable which is going to store the sum of these values. Next, we create a for statement containing firstly type and identifier (int x). Using a colon, we set this equal to the name of the array we're working with (aryOne). What this does is loops all the indices in the array and for each iteration, the current index is stored in x. We add them together like so: total += x;. Too easy.

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Array Elements As Counters - JavaDevelopmentForums.com

OA-OD-JD1 — Sun, 29 Jan 2012 22:07:23 GMT

We're going to build a program to re-enact a dice being rolled one thousand times. We're going to output how many times each face of the dice is rolled.
import java.util.Random;
 
class RollDice{
   public static void main(String args[]){
	   Random rand = new Random();
	   int freq[] = new int[7];
 
	   for(int roll = 1; roll <= 1000; roll++){
		   ++freq[1 + rand.nextInt(6)];
	   }
	   System.out.println("Face\tFrequency");
	   for(int face = 1; face < freq.length; face++){
		   System.out.println(face + "\t" + freq[face]);
	   }
   }
}
First of all, we have to import our random class. Then, we create a new random number object called rand. We create a new integer array called freq. We set this equal to 7 because we want the numbers 1-6. 7 Will give us 0-6 but we'll just ignore the zero.

Next up is our for loop set to iterate one thousand times. In that we increment the index of our frequency array by a random number ranging from 1 through to 6. This line of code stores the values of each face of the die.

We then output a header (face and frequency) separated by a tab and create a small for loop to output the face and value of each face. This is really just six iterations.

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Summing The Elements of An Array

OA-OD-JD1 — Sun, 29 Jan 2012 22:02:01 GMT

Say we have an array with ten indices. Below is how we can calculate the sum of these indices.
class Class1{
	public static void main(String args[]){
		int[] array1 = {1,2,3,4,5,6,7,8,9,10};
		int total = 0;
 
		for(int counter = 0; counter < array1.length; counter++){
			total += array1[counter];
		}
 
		System.out.println("Total\t" + total);
 
	}
}
Firstly, initialise your array. Then, create a variable to store the total. A simple For Loop set to iterate to the length of our array will do the trick. All you need to do is set the total to the total plus the array with the index if the current counter. A very simple concept.

In an unrelated topic, I'm now up to my 30th Java tutorial. I'm making some nice leadway here, though I've still got a heck of a lot to learn.

Arrays

OA-OD-JD1 — Sun, 29 Jan 2012 22:01:00 GMT

Arrays are used to store many values under the one variable, so to speak. You can initialise an array the long and drawn out way by manually assigning each index a value or you can implement an array initialiser to do the job for you.
class Class1{
	public static void main(String args[]){
		int array1[] = new int[10];
		array1[0] = 87;
		array1[1] = 543;
		array1[2] = 65;
		System.out.println(array1[2]);
 
		int array2[] = {1,2,3,4,5,6,7,8};
		System.out.println(array2[4]);
 
	}
}
In this example, array1 is the slow way, and array2 makes use of an array initialiser. To build an array, you must first create the variable. You do this by typing the data type (int) followed by the array name (array1) and then add two square brackets ([]) to show that we're working with an array. Set this equal to a new int (if that is the chosen data type) followed by the number of indices in square brackets. That's the slow way of course.

You can use an array initialiser as follows. Data Type arrayName[] = {index1, index2, index3, etc};. That's a much easier was of going about building an array.

Random Number Generator

OA-OD-JD1 — Sun, 29 Jan 2012 22:00:35 GMT

Random numbers can be used in Java. Here's a small random number generator and how it works.
import java.util.Random;
class Class1{
	public static void main(String args[]){
		Random dice = new Random();
		int number;
 
		for(int counter = 1; counter <= 10; counter++){
			number = dice.nextInt(6) + 1;
			System.out.println(number);
		}
	}
}
First of all, we need to import the random class. Type import java.util.Random; at the top of your code. We then created an object to use this random numer and we named it dice. We made an integer named number to store this value. We then created a loop iterating ten times and each time it did we assigned number a new random number using our dice object. We did this by typing dice.nextInt(6) + 1;. The reason we've added one to the output is to prevent us from receiving numbers 0-5. We want numbers 1-6, so we simply add one to the output.

Math Class Methods

OA-OD-JD1 — Sun, 29 Jan 2012 22:00:10 GMT

There are many built in methods we can use to conduct mathematical operations to numbers. Here are some of them.

class Class1{
	public static void main(String args[]){
		//How far number is from zero.
		System.out.println(Math.abs(-26.7));
		//Rounds number up.
		System.out.println(Math.ceil(7.4));
		//Rounds number down.
		System.out.println(Math.floor(7.8));
		//Greater of the two numbers.
		System.out.println(Math.max(8.6, 5.2));
		//Smaller of the two numbers.
		System.out.println(Math.min(8.6, 5.2));
		//First number to the power of the second number.
		System.out.println(Math.pow(5, 3));
		//Square root of the number.
		System.out.println(Math.sqrt(9));
	}
}

All pretty self explanatory.

Do While Loop

OA-OD-JD1 — Sun, 29 Jan 2012 21:58:06 GMT

We use the Do While Loop when we want to run a set of instructions before testing to see if a condition is true. The difference between a Do While Loop and a While Loop is that the While Loop tests the condition first and then runs the instructions.
class Class1{
	public static void main(String args[]){
		int counter = 0;
		do{
			System.out.println(counter);
			counter++;
		}while(counter <= 10);
	}
}
We have a counter initialised to zero. It's going to then output the counter as zero and then increment it by 1. It then checks to see if the while section will permit it to iterate again.

If our counter had been initialised to 50, it would output 50 and then end, because the while section sees that the counter isn't actually <= 10.

The only perameter used in the while part is when you want it to iterate. In this case it's while the counter is less than or equal to 10. Simple enough?

Compound Interest Calculator

OA-OD-JD1 — Sun, 29 Jan 2012 21:57:47 GMT

Compound interest can be calculated with the following formula.

A = Amount
P = Principal
R = Rate
n = Years

A=P(1+R)^n

We can calculate the amount in Java as shown below. We currently know the principal (10,000) and the rate (1%). The years can change depending on how much information we want. In this application, we'll just use 20.
class Class1{
	public static void main(String args[]){
		double amount;
		double principal = 10000;
		double rate = .01;
 
		for(int year = 1; year <= 20; year++){
			amount = principal * Math.pow(1+ rate, year);
			System.out.println(year + "  " + amount);
		}
	}
}
We initialise our variables as per usual. We then construct a For Loop which will give us 20 iterations. Using our formula, we calculate the amount. We used the Math.pow function because it allows us to use indices. The first parameter is what you want in the parentheses and the second parameter is what you want the power to be. Quite a simple calculator.

For Loops

OA-OD-JD1 — Sun, 29 Jan 2012 21:57:29 GMT

The For Loop is probably the most common loop used in any programming language. Here's how it works in Java.
class Class1{
	public static void main(String args[]){
		for(int counter=1; counter<=10; counter++){
			System.out.println(counter);
		}
	}
}
The For Loop takes three arguments: where you want it to start, where you want it to end, and how you'd like to increment the counter. Take a look at the below For Loop setup.

for(int counter=1; counter<=10; counter++)

What this is saying is that it's going to start at 1. It's going to keep running until it reaches 11 (that's ten iterations). And it's going to increment the counter by one each time. Pretty simple.

Simple Averaging Program

OA-OD-JD1 — Sun, 29 Jan 2012 21:56:18 GMT

What this application does is collects a number of inputs from the user via a scanner. These inputs are numbers. They are then averaged and the average is outputted. Pretty simple stuff.
import java.util.Scanner;
class Class1{
	public static void main(String args[]){
		Scanner input = new Scanner(System.in);
		int total = 0;
		int grade;
		int average;
		int counter = 0;
		int numGrades = 10;
 
		System.out.println("Please enter " + numGrades + " numbers to be averaged");
		while(counter < numGrades){
			grade = input.nextInt();
			total = total + grade;
			counter++;
		}
		average = total/numGrades;
		System.out.println("Your average is " + average + ".");
	}
}
How could I change this to make it more challenging to create? I could have used multiple classes or multiple methods to do various tasks. For example, one method could be used to loop through the inputs, and another could be used to find the average. In fact, I'm going to do this now. Check it out.
import java.util.Scanner;
class Class1{
	public static void main(String args[]){
		int numGrades = 10;
		System.out.println("Please enter " + numGrades + " numbers to be averaged");
		//Start loop/average method
		Class1 class1Object = new Class1();
		class1Object.loopAverage(numGrades);
	}
	public void loopAverage(int numGrades){
		int grade;
		int counter = 0;
 
		int total = 0;
		int average;
		Scanner input = new Scanner(System.in);
 
		while(counter < numGrades){
			grade = input.nextInt();
			total = total + grade;
			counter++;		
		}
		average = total/numGrades;
		System.out.println("Your average is " + average + ".");		
	}
}
I managed to use the main method for the introduction and to call the second method. I tried using three methods, one for the main method, one for the loop, and one for the average, however, when I tried sending variables from the loop method to the average method, it was reading the variables from the main method. I wasn't sure how to go about fixing this, so if anyone could help out, I'd really appreciate that. I'll look into it myself now.

Maybe I could use something like this.
public String getTotal(){
   return total;
}
But then how would this know to get the total from the loop method and not the main method? And I want to send the total from the loop method and the numGrades from the main method? Not sure how to go about doing this.

Scanners

OA-OD-JD1 — Sun, 29 Jan 2012 21:55:57 GMT

I forgot to write about the scanner, so I'm going to do that now.

Basically, a scanner is used to get information from the user. At this stage, the scanner will be used only to gather information from the keyboard. Here's how it works.
import java.util.Scanner;
class Class1{
	public static void main(String args[]){
		Scanner input = new Scanner(System.in);
		System.out.println("Enter some text:");
		System.out.println("The text you entered was: " + input.nextLine());		
	}
}
Firstly, we must import the scanner, since it's not available in the default library. It's found in the java.util library, so we write import java.util.Scanner; at the top of our code to allow us to use the scanner. Capitalisation here is important.

Next, we need to create a new scanner variable to let us use the scanner. Do this by typing Scanner followed by the name of the object (in this case, I called mine input). Set the object equal to new Scanner with the parameter of System.in - this allows us to read the keyboard input.

Now whenever you type into the console (or other field), the text you enter before pressing enter will be stored in the input scanner variable. To output this, we need to figure out what data type we're working with. In this case, it's a string of text so we use input.nextLine(). That's really all there is to it!

JD1's Personal Development Blog

OA-OD-JD1 — Sun, 29 Jan 2012 21:54:04 GMT

Originally Posted by KevinWorkman

Again, just to nitpick, the tertiary (conditional) operator isn't exactly like an if statement- it simply chooses between two values. You can't, for example, do this:

boolean blue = true;
blue ? System.out.println("blue") : System.out.println("red");

Instead, you'd have to do something like this:

boolean blue = true;
String print = blue ? "blue" : "red";
System.out.println(print);

20 Tutorials Summarised!

OA-OD-JD1 — Sun, 29 Jan 2012 21:53:16 GMT

Well, I've finally finished watching and summarising (in this thread) the first twenty tutorials of TheNewBoston's Java Programming Tutorial series. I've previously watched all 87 tutorials, but never summarised any of them to the point that the information stuck in my head long enough for me to retain.

I plan on doing the same sort of thing for the next 67 tutorials and then into the Intermediate Java tutorials.

Thank you to everyone who has helped me out along the way. I have a long way to go but that will be made much easier with your continued support.

Thanks,
JD1

Conditional Operators

OA-OD-JD1 — Sun, 29 Jan 2012 21:52:59 GMT

Basically, I like to look at Conditional Operators as a quick way of implementing an If Statement. That's really all they are. Take a look at this code.
class Class1{
	public static void main(String[] args){
		int age =50;
		System.out.println(age > 30 ? "You are quite old!" : "You are still young!");
	}
}
You can see that we've initalised an integer with the value of 50. Our Conditional Operator then checks to see if it's greater than thirty (age > 30 ?). We use a question mark to see if the condition is true. You then write the true and false outputs separated by a colon. That's really all there is to it!

Constructors

OA-OD-JD1 — Sun, 29 Jan 2012 21:52:40 GMT

We can use a constructor to quickly initialise variables as soon as our object is created. If you haven't read the above post, please do - you will become familiar with the code we're using for these examples.

Here's Class1.
class Class1{
	public static void main(String args[]){
		Class2 class2Object = new Class2("Tony");
		class2Object.outputName();
	}
}
You can see what we've done here is added an argument of "Tony" to our class2Object. To use this constructor, you must make a method with the exact same name as the class in which it's in. Take a look at our Class2 code.
public class Class2 {
	private String friendName;
 
	public Class2(String name){
		friendName = name;
	}
	public void setName(String name){
		friendName = name;
	}
	public String getName(){
		return friendName;
	}
	public void outputName(){
		System.out.printf("Your friend's name is %s", getName());
	}
}
You will notice this new method.
public Class2(String name){
		friendName = name;
	}
The method's name is Class2, identicle to that of our class name. Since we were able to send the name variable over to Class2 as the object was created, this now makes our setName method redundant. Its job has been taken care of.

Constructors are useful if we wanted to use multiple objects. Each object has its own set of variables. What we could do, if we wanted, would be to create another object like this.
Class2 class2Object2 = new Class2("Betty");
We could now decide to output class2Object2 or class2Object1; each would produce a different output.