java tutorial - Учебники java - учебник java - java programming - учиться java - java basics - java for beginners

sudo add-apt-repository ppa:webupd8team/java

sudo apt-get install software-properties-common 
sudo add-apt-repository ppa:webupd8team/java

sudo apt-get update

sudo apt-get install oracle-java8-installer

java -version

java -version

-vm
C:\DevPrograms\Java\jdk1.8.0_45\bin\javaw.exe

java -version
 
dpkg --print-architecture

package org.wikitechy.tutorial.javabasic.variable;
 
public class VariableExample1 {
 
    public static void main(String[] args) {
 
        // Declare a variable of type int (integer 32-bit)
        int firstNumber;
 
        // Assigning values to firstNumber
        firstNumber = 10;
 
        System.out.println("First Number =" + firstNumber);
 
        // Declare a 32-bit real number (float)
        // This number is assigned a value of 10.2
        float secondNumber = 10.2f;
 
        System.out.println("Second Number =" + secondNumber);
 
        // Declare a 64-bit real numbers
        // This number is assigned a value of 10.2
        // character d at the end to tell with Java this is the type double.
        // Distinguished from a float.
        double thirdNumber = 10.2d;
 
        System.out.println("Third Number =" + thirdNumber);
 
        // Declare a character
        char ch = 'a';
 
        System.out.println("Char ch= " + ch);
 
    }
 
}

package org.wikitechy.tutorial.javabasic.variable;
 
public class VariableExample2 {
 
    public static void main(String[] args) {
 
        // Declare three 64-bit integer (long)
        long firstNumber, secondNumber, thirdNumber;
 
        // Assign value to firstNumber
        // L at the end to tell java a long type, distinguished from type int.
        firstNumber = 100L;
 
        // Assign values to secondNumber
        secondNumber = 200L;
 
        // Assign values to thirdNumber
        thirdNumber = firstNumber + secondNumber;
 
        System.out.println("First Number = " + firstNumber);
        System.out.println("Second Number = " + secondNumber);
        System.out.println("Third Number = " + thirdNumber);
    }
 
}

if(condition1 true)  {
 // Do something here
}else if(condition2 true) {
 // Do something here
}else if(condition3 true) {
 // Do something here
}else  { // Other
 // Do something here
}

package org.wikitechy.tutorial.javabasic.controlflow;
 
public class ElseIfExample1 {
 
    public static void main(String[] args) {
         
        // Declaring a integer number (int)        
        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!");
        }
 
    }
}

int score = 20;

package org.wikitechy.tutorial.javabasic.controlflow;
 
public class ElseIfExample2 {
 
    public static void main(String[] args) {
 
        // Declare a variable int simulate your age.
        int age = 20;
 
        // Test 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 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");
            }
 
        }
 
    }
}

package org.wikitechy.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");
        }
 
        // With boolean values you can also write
        if (value) {
            System.out.println("It's true");
        }
        // Else
        else {
            System.out.println("It's false");
        }
    }
}

switch ( variable_to_test ) {
  case value:
   // code_here;
   break;
  case value:
   // code_here;
   break;
  default:
   // values_not_caught_above;
}

package org.wikitechy.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");
        }
 
    }
 
}

// This is not allowed !!
case (age < 18) :
 
// case only accept a specific value eg:
case 18:
  // Do something here
  break;

package org.wikitechy.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");
 
        // 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");
        }
 
    }
 
}

for ( start_value; end_value; increment_number ) {
  // Code here
}

package org.wikitechy.tutorial.javabasic.loop;
 
public class ForLoopExample1 {
 
    public static void main(String[] args) {
 
        // Declare a variable, 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;
 
        }
 
    }
 
}

package org.wikitechy.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 loop 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);
 
    }
 
}

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

package org.wikitechy.tutorial.javabasic.loop;
 
public class WhileExampe1 {
 
     
    public static void main(String[] args)  {
         
        int value = 3;
         
        // While the value is less than 10, the loop is working.
        while( value < 10)  {
             
            System.out.println("Value = "+ value);
             
            // Increase value by adding 2
            value = value + 2;
        }
    }
}

// The do-while loop to work at least one round
// and while the condition is true, it also works to
do {
  // Do something here.
}
while ( condition );

package org.wikitechy.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 3
           value = value + 3;
 
       } while (value < 10);
 
   }
}

// Declare an array, not a specified number of elements.
int[] array1;
 
 
// Initialize the array with 100 elements
// The element has not been assigned a specific value
array1 = new int[100];
 
// Declare an array specifies the number of elements
// The element has not been assigned a specific value
double[] array2 = new double[10];
 
// Declare an array whose elements are assigned specific values.
// This array with 4 elements
long[] array3= {10L, 23L, 30L, 11L};

package org.wikitechy.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 values to the second element (index 1)
        myArray[1] = 14;
         
        myArray[2] = 36;
        myArray[3] = 27;
         
        // Value for 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]);    
        }
    }
}

package org.wikitechy.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]);
    }
}

package org.wikitechy.tutorial.javabasic.javastructure;
 
public class Person {
 
     
    // This is field
    // The name of Person
    public String name;
     
    // This is a Constructor
    // Use it to initialize the object (Create new object)
    // This constructor has one parameter
    // Constructor always have the same name as the class.
    public Person(String persionName) {
        // Assign the value of the parameter into the 'name' field
        this.name = persionName;
    }
 
    // This method returns a String ..
    public String getName() {
        return this.name;
    }
 
}

package org.wikitechy.tutorial.javabasic.javastructure;
 
public class PersonTest {
 
   public static void main(String[] args) {
 
       // Create an object of class Person
       // Initialize this object via constructor of class Person
       // Specifically, Edison
       Person edison = new Person("Edison");
 
       // Class Person has the method getName()
       // Use the object to call getName():
       String name = edison.getName();
       System.out.println("Person 1: " + name);
 
       // Create an object of class Person
       // Initialize this object via constructor of class Person
       // Specifically, Bill Gates
       Person billGate = new Person("Bill Gates");
 
       // Class Person has field name (public)
       // Use objects to refer to it.
       String name2 = billGate.name;
       System.out.println("Person 2: " + name2);
 
   }
 
}

package org.wikitechy.tutorial.javabasic.javastructure;
 
public class FieldSample {
     
    // This is static field.
    public static int MY_STATIC_FIELD = 100;
     
    // This is normal field.
    public String myValue;
     
     
    // Constructor
    public FieldSample(String myValue)  {
        this.myValue= myValue;
    }
 
}

package org.wikitechy.tutorial.javabasic.javastructure;
 
public class FieldSampleTest {
 
    public static void main(String[] args) {
 
        // Create the first object.
        FieldSample obj1 = new FieldSample("Value1");
 
        System.out.println("obj1.myValue= " + obj1.myValue);
 
        // Print out static value, access via instance of class (an object).
        System.out.println("obj1.MY_STATIC_FIELD= " + obj1.MY_STATIC_FIELD);
 
        // Print out static value, access via class.
        System.out.println("FieldSample.MY_STATIC_FIELD= "
                + FieldSample.MY_STATIC_FIELD);
 
        // Create second object:
        FieldSample obj2 = new FieldSample("Value2");
 
        System.out.println("obj2.myValue= " + obj2.myValue);
 
        // Print out static value, access via instance of class (an object)
        System.out.println("obj2.MY_STATIC_FIELD= " + obj2.MY_STATIC_FIELD);
 
        System.out.println(" ------------- ");
 
        // Set new value for static field.
        // (Or using: FieldSample.MY_STATIC_FIELD = 200)
        obj1.MY_STATIC_FIELD = 200;
 
        // It will print out the value 200.
        System.out.println("obj2.MY_STATIC_FIELD= " + obj2.MY_STATIC_FIELD);
    }
}

package org.wikitechy.tutorial.javabasic.javastructure;
 
public class FinalFieldExample {
 
    // A final field.
    // Final Field does not allow to assign new values.
    public final int myValue = 100;
 
    // A static final field.
    // Final field does not allow to assign new values.
    public static final long MY_LONG_VALUE = 1234L;
}

package org.wikitechy.tutorial.javabasic.javastructure;
 
public class MethodSample {
 
    public String text = "Some text";
     
    // Default Constructor
    public MethodSample()  {
         
    }
 
    // This method return a String
    // and has no parameter.
    public String getText() {
        return this.text;
    }
 
    // This is a method with one parameter String.
    // This method returns void (not return anything)    
    public void setText(String text) {
        // this.text reference to the text field.
        // Distinguish the text parameter.        
        this.text = text;
    }
 
    // Static method
    public static int sum(int a, int b, int c) {
        int d =  a + b + c;
        return d;
    }
}

package org.wikitechy.tutorial.javabasic.javastructure;
 
public class MethodSampleTest {
 
    public static void main(String[] args) {
 
        // Create instance of MethodSample
        MethodSample obj = new MethodSample();
 
        // Call getText() method
        String text = obj.getText();
 
        System.out.println("Text = " + text);
 
        // Call method setText(String)
        obj.setText("New Text");
 
        System.out.println("Text = " + obj.getText());
 
        // Static method can be called through the class.
        // This way is recommended. (**)
        int sum = MethodSample.sum(10, 20, 30);
 
        System.out.println("Sum  10,20,30= " + sum);
 
        // Or call through objects
        // This way is not recommended. (**)        
        int sum2 = obj.sum(20, 30, 40);
 
        System.out.println("Sum  20,30,40= " + sum2);
    }
 
}

package org.wikitechy.tutorial.javabasic.inheritance;
 
public class Animal {
 
 public Animal() {
 
 }
 
 public void move() {
     System.out.println("Move ...!");
 }
 
 public void say() {
     System.out.println("<nothing>");
 }
 
}

package org.wikitechy.tutorial.javabasic.inheritance;
 
public class Cat extends Animal {
 
    // Override method of the Animal class.
    public void say() {
        System.out.println("Meo");
    }
}

package org.wikitechy.tutorial.javabasic.inheritance;
 
public class Dog extends Animal {
 
   // Override method of the Animal class.
   public void say() {
       System.out.println("Go");
   }
}

package org.wikitechy.tutorial.javabasic.inheritance;
 
public class Ant extends Animal {
 
}

package org.wikitechy.tutorial.javabasic.inheritance;
 
public class AnimalTest {
 
    public static void main(String[] args) {
 
        // Declaring a Cat object.
        Cat cat = new Cat();
 
        // Check 'cat' instance of Animal.
        // The result is clearly true.
        boolean isAnimal = cat instanceof Animal;
        System.out.println("cat instanceof Animal?"+ isAnimal);
 
        // ==> Meo
        // Call the method say() of the Cat.
        cat.say();
 
 
        // Declare an object Animal
        // Initialize the object through the Constructor of the Cat.
        Animal cat2 = new Cat();
 
        // ==> Meo
        // Call to say() of Cat (Not Animal)
        cat2.say();
 
        // Create the object Animal
        // Through the Constructor of the class Ant.        
        Animal ant = new Ant();
 
        // Ant has no say() method.
        // It call to say() method that inherited from the parent class (Animal)        
        ant.say();
    }
}