Week 2: Java fundamentals

 

2.1 Basic Java Application Format

Learn From Our First Application

/*
 * U of M Hello world
 */

// This is a program that will say hello world

public class FirstProgram
{
   public static void main(String[] args)
   {
     System.out.println("U of M Hello World");
   }
}

 

We need:

Other Required Source Code Format

 

2.2 Basic Programming Construct for Java Language

Data types

Strongly type language: variable must has declared type. There are eight primitive types. Six of them are numbers, one is character (used in Unicode), and one is a boolean.

Integral types

Type Storage Range
byte 1 byte -128 to 127
short 2 bytes -32768 to 32767
int 4 bytes -2147483648 to 2147483647
long 8 bytes "Really small" to "Really big"

Note:
The integer types do not depend on the machine on which you will be running Java code, only performance will vary.
The sizes of all numeric types are platforms independent. (not 2 or 4).
Long integer has L suffix (e.g. 400000000L), Hex numbers has prefix 0xABCD.

Floating point types

Type Storage Precision
float 4 bytes 6-7 significant digits
double 8 bytes 15 significant digits

Note:
double implies twice precision as float. (e.g. Use in matrix computation)
float literal has suffix F.
default will be used as double.

Character Types

Boolean

2.3 More Construct - Variables

Examples: 

int a;
float b;
char ch1, ch2, thisIsALongVariableName;
boolean flag;
int size;

Assignments and Initializations

int i = 10;
int foo; // this is a declaration
foo = 37; // this is an assignment
char myvar = '\u0041'; // decimal 65 => this is actually a A

Numeric Types Casting (Conversions)

Constant

Operators

2.4 From Basic Construct (build-in type) to Class - Strings

Examples:

String firstName;
firstName = "Richard";
String lastName = "Sinn";

// Initializes fullName to "Richard Sinn":
String fullName = firstName + " " + lastName;

// Print out some strings:
System.out.print ("Your instructor's name is: ");
System.out.println (fullName);

// Initializes s1 to "d S":
// 6 is the first you want to copy
// 9 is the first one you do not want to copy
// Start from 0
// Length is 9-6 = 3
String s1 = fullName.substring (6, 9);

// Initializes nameLength to 12:
int nameLength = fullName.length ();

// Initializes ch to 'c':
// Range from 0 to fullName()-1
char ch = fullName.charAt (2);

// Replacement Example:
String greeting = "Hello";
greeting = greeting.substring(0, 3) + "p!"; // Help!

// Examples of comparisons:
// == indicates whether the String stores in the same place
// *ALWAYS* use equals to compare
String copy1 = fullName;
String copy2 = "Richard Sinn";
boolean testA = (copy1 == fullName); // true
boolean testB = (copy2 == fullName); // false
boolean testC = copy1.equals (fullName); // true
boolean testD = copy2.equals (fullName); // true

// Initializes i1 to 8 and i2 to -1:
// remember counting starts with 0
int i1 = fullName.indexOf (lastName);
int i2 = fullName.indexOf ("Carmen");

// Page 70 for more functions

2.5 More Fundamental Programming Structures in Java - Control Flow

Conditionals (a.k.a. "if-then-else")

Syntax: 






if (condition)





{





	block





}





else 





{





	block2





}

Examples: 

int temperature;  // Assume it gets initialized somehow.

if (temperature < 32)
	System.out.println ("It is cold.");

boolean move = false;
if (temperature < 0)
{
  	System.out.println ("It is so cold that I will move to CA.");
	move = true;
}

if (move)
	System.out.println ("I am selling my house.");
else
	System.out.println ("I am staying put.");

boolean wearCoat;
if (temperature >= 60) 
{
	System.out.println ("I am happy again.");
	wearCoat = false;
}	
else
{
	System.out.println ("It is chilly.");
	wearCoat = true;
}

While loops

Examples: 

int i = 0;
while ((i * i) != 81)
	++i;
System.out.println ("The square root of 81 is: " + i);

int j = 0;
while (j < 10) 
{
	System.out.println ("j = " + j);
	++j;
}

Do-while loops

Examples: 

char ch = 'z';
do 
{
	System.out.print (ch);
	--ch;
} while (ch != 'a');

// Loop doing the same thing
while (ch != 'a')
{
	System.out.print (ch);
	--ch;
}

For loops

Examples: 

int sum = 0;
for (int i = 1; i <= 100; ++i)
	sum += i;

int loops = 0;
for (int j = 1000; j > 0; j /= 2)
{
	System.out.println ("j = " + j);
	++loops;
}
System.out.println ("It took " + loops + " loops.");

Switch-case

Example: 

int day; // Assume this was initialized somewhere.
boolean exerciseDay = false;
boolean weekend = false;

switch (day)
{
	case 1; // Monday
		System.out.println("Monday ... Arr ... sucks");
		break;
	case 2: // Tuesday
		exerciseDay = true;
		break;
	case 4: // Thursday
		exerciseDay = true;
		break;
	case 0: // Sunday
		break;
	case 6: // Saturday
		weekend = true;
		break;
	default: // Everything else.
		System.out.println ("Ordinary work day.");
		break;		
}

2.6 Functions

Normal Function 

// This function adds all numbers from 1 to the argument
// and returns the sum.
int computeSum (int arg)
{
	int sum = 0;
	for (int i = 1; i <= arg; ++i)
		sum += i;
	return sum;
}


// This function prints out all of the sums for each
// odd number from 1 to 19.
void functionB ()
{
	for (int i = 1; i <= 19; i += 2)
		System.out.println ("computeSum(i)=" + computeSum (i));
}

Main function

Example: 

public static void main (String[] args)
{
	// Print out the hello world
	System.out.println("Testing - Hello World");
}

2.7 Arrays

Examples: 

int[] temperatures = new int[31];
temperatures[0] = 45;
temperatures[1] = 52;
temperatures[2] = 53;
// ... and so on.

System.out.println ("The temperature on day 15 was " 
	+ temperatures[14]);

int sum;
for (int i = 0; i < temperatures.length; ++i)
	sum += temperatures[i];
float avg = sum / temperatures.length;

// colors will be an array of length 4:
String[] colors = { "red", "green", "blue", "orange" };

// Main function example
public static void main (String[] args)
{
	// Print out the command line arguments.
	for (int i = 0; i <. args.length; ++i)
		System.out.println ("Argument " + i + "=" + args[i]);
}

Lab

Create a Java application (called Week2) that critiques a student based on his or her grade. The students name and grades are input to the application as command line arguments, in the following form: 

java Week2 Sinn,Richard 98 97 96 96 95

Your application should contain five functions:

A few notes:

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