Tutoriel Java pour les débutants

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• Types de données dans Java

5.1- if-else statement

The structure of an if-else statement is:

if(condition 1)  {
   // Do something here
}else if(condition 2) {
   // Do something here
}else if(condition 3) {
   // Do something here
}
// Else
else  { 
   // Do something here
}

Create class ElseIfExample1:

ElseIfExample1.java

package org.o7planning.tutorial.javabasic.controlflow;

public class ElseIfExample1 {

	public static void main(String[] args) {

		// Declaring a varible of type int (32 bit integer)
		// Represent your test scores.
		int score = 20;

		System.out.println("Your score =" + score);

		// If the score is less than 50
		if (score < 50) {
			System.out.println("You are not pass");
		}
		// Else if the score more than or equal to 50 and less than 80.
		else if (score >= 50 && score < 80) {
			System.out.println("You are pass");
		}
		// Remaining cases (that is greater than or equal to 80)
		else {
			System.out.println("You are pass, good student!");
		}

	}
}

Results of running the class ElseIfExample1:

Change the value of the variable "score" in the above example and rerun the class ElseIfExample1:

int score = 20;

5.2- The normal operator

• > Greater Than
• < Less Than
• >= Greater Than or Equal To
• <= Less Than or Equal To
• && AND
• || OR
• == HAS A VALUE OF
• != Not Equal To
• ! NOT

Create class ElseIfExample2

ElseIfExample2.java

package org.o7planning.tutorial.javabasic.controlflow;

public class ElseIfExample2 {

	public static void main(String[] args) {

		// Declare a variable of type int, represents your age.
		int age = 20;

		// Test if age less than or equal 17
		if (age <= 17) {
			System.out.println("You are 17 or younger");
		}

		// Test age equals 18
		else if (age == 18) {
			System.out.println("You are 18 year old");
		}
		// Test if age greater than 18 and less than 40
		else if (age > 18 && age < 40) {
			System.out.println("You are between 19 and 39");
		}
		// Remaining cases (Greater than or equal to 40)
		else {
			// Nested if statements
			// Test age not equals 50.
			if (age != 50) {
				System.out.println("You are not 50 year old");
			}

			// Negative statements
			if (!(age == 50)) {
				System.out.println("You are not 50 year old");
			}

			// If age is 60 or 70
			if (age == 60 || age == 70) {
				System.out.println("You are 60 or 70 year old");
			}

		}

	}
}

You can change the value of "age" and rerun ElseIfExample2 class and see the results

5.3- Boolean value

boolean is a data type, it only has two values true or false.

Create class BooleanExample:

BooleanExample.java

package org.o7planning.tutorial.javabasic.controlflow;

public class BooleanExample {

	public static void main(String[] args) {

		// Declare a variable of type boolean
		boolean value = true;

		// If value is true
		if (value == true) {
			System.out.println("It's true");
		}
		// Else
		else {
			System.out.println("It's false");
		}


		if (value) {
			System.out.println("It's true");
		}
		// Else
		else {
			System.out.println("It's false");
		}
	}
}

5.4- switch- case -default statement

This is also a branch statement similar to the if-else is introduced above

// variable_to_test: A varible to test.
switch ( variable_to_test ) {
  case value1:
   // Do something here ...
   break;
  case value2:
   // Do something here ...
   break;
  default:
   // Do something here ...
}

SwitchExample1.java

package org.o7planning.tutorial.javabasic.controlflow;

public class SwitchExample1 {

	public static void main(String[] args) {

		// Declare a variable age
		int age = 20;

		// Check the value of age
		switch (age) {
		// Case age = 18
		case 18:
			System.out.println("You are 18 year old");
			break;
		// Case age = 20
		case 20:
			System.out.println("You are 20 year old");
			break;
		// Remaining cases
		default:
			System.out.println("You are not 18 or 20 year old");
		}

	}

}

The results of running the class SwitchExample1:

Note that the case statement is a specific value you can not do the following:

// This is not allowed !!
case (age < 18) :

// case only accept a specific value, eg:
case 18:
  // Do something here ..
  break;

See an example:

SwitchExample2.java

package org.o7planning.tutorial.javabasic.controlflow;

public class SwitchExample2 {

	public static void main(String[] args) {

		// Declare a variable age.
		int age = 30;

		// Check the value of age.
		switch (age) {
		// Case age = 18
		case 18:
			System.out.println("You are 18 year old");
			break;
		// Case age in 20, 30, 40
		case 20:
		case 30:
		case 40:
			System.out.println("You are " + age);
			break;
		// Remaining case:
		default:
			System.out.println("Other age");
		}

	}

}

The results run:

5.5- for Loop

Syntax:

// start_value: Start Value
// end_value: End Value
// increment_number: Added value after each iteration.
for ( start_value; end_value; increment_number ) {
   // Do something here
}

Consider an illustration:

ForLoopExample1.java

package org.o7planning.tutorial.javabasic.loop;

public class ForLoopExample1 {

	public static void main(String[] args) {

		// Declare a variable 'step', step in loop
		int step = 1;

		// Declare a variable value with the start value is 0
		// After each iteration, value will increase 3
		// And the loop will end when the value greater than or equal to 10
		for (int value = 0; value < 10; value = value + 3) {

			System.out.println("Step =" + step + "  value = " + value);

			// Increase 1
			step = step + 1;

		}

	}

}

Results of running the class ForLoopExample1:

See another example, sum the numbers from 1 to 100:

ForLoopExample2.java

package org.o7planning.tutorial.javabasic.loop;

public class ForLoopExample2 {

	// This is an example to sum the numbers from 1 to 100,
	// and print out the results to the console.
	public static void main(String[] args) {

		// Declare a variable
		int total = 0;

		// Declare a variable value
		// Initial value is 1
		// After each iteration increases the 'value' by adding 1
		// Note: value++ equivalent to the statement: value = value + 1;
		// value-- equivalent to the statement: value = value - 1;
		for (int value = 1; value <= 100; value++) {

			// Increase 'total' by adding 'value'.
			total = total + value;
		}

		System.out.println("Total = " + total);

	}

}

Result:

5.6- while Loop

This is while loop structure:

// While condition is true then do something.
while ( condition ) {
   // Do something here...
}

See illustration

WhileExample1.java

package org.o7planning.tutorial.javabasic.loop;

public class WhileExampe1 {

	public static void main(String[] args) {

		int value = 3;

		// While the 'value' is still less than 10, the loop still works.
		while (value < 10) {

			System.out.println("Value = " + value);

			// Increase 'value' by adding 2
			value = value + 2;
		}
	}
	
}

5.7- do-while Loop

This is the structure do-while loop:

// The do-while loop performs at least one iteration.
// And while the condition is true, it continues to work
do {
   // Do something here.
}
while (condition);

Example:

DoWhileExample1.java

package org.o7planning.tutorial.javabasic.loop;

public class DoWhileExample1 {

	public static void main(String[] args) {

		int value = 3;

		// do-while loop will execute at least once
		do {

			System.out.println("Value = " + value);

			// Increase by 3
			value = value + 3;

		} while (value < 10);

	}
}

Result:

6.1- What is Array?

An array is a list of the elements are arranged adjacent to each other in memory.

Let's see, a array with 5 elements, int type.

6.2- Working with arrays

How to declare an array in Java.

// Declare an array, not a specified number of elements.
int[] array1;

// Initialize the array with 100 elements
// The elements has not been assigned a specific value
array1 = new int[100];

// Declare an array specifies the number of elements
// The elements has not been assigned a specific value
double[] array2 = new double[10];

// Declare an array with elements assigned a specific values.
// This array has 4 elements
long[] array3= {10L, 23L, 30L, 11L};

Let's look at an example:

ArrayExample1.java

package org.o7planning.tutorial.javabasic.array;

public class ArrayExample1 {

	public static void main(String[] args) {

		// Declare an array with 5 elements
		int[] myArray = new int[5];

		// Note: the first element of the array index is 0:
		// Assigning values to the first element (index 0)
		myArray[0] = 10;

		// Assigning value to the second element (index 1)
		myArray[1] = 14;

		myArray[2] = 36;
		myArray[3] = 27;

		// Assigning value to the 5th element (the last element in the array)
		myArray[4] = 18;

		// Print out element count.
		System.out.println("Array Length=" + myArray.length);

		// Print to Console element at index 3 (4th element in the array)
		System.out.println("myArray[3]=" + myArray[3]);

		// Use a for loop to print out the elements in the array.
		for (int index = 0; index < myArray.length; index++) {
			System.out.println("Element " + index + " = " + myArray[index]);
		}
	}

}

Result:

An illustrative example to use a for loop to assign values to the elements:

ArrayExample2.java

package org.o7planning.tutorial.javabasic.array;

public class ArrayExample2 {

	public static void main(String[] args) {

		// Declare an array with 5 elements
		int[] myArray = new int[5];

		// Print out element count
		System.out.println("Array Length=" + myArray.length);

		// Using loop assign values to elements of the array.
		for (int index = 0; index < myArray.length; index++) {
			myArray[index] = 100 * index * index + 3;
		}

		// Print out the element at index 3
		System.out.println("myArray[3] = " + myArray[3]);
	}

}

Result: