Java

hello world

public class aplication {

	public static void main(String[] args) {
		System.out.println("Hello world!");
		

	}

}

variables

public class variables {

	public static void main(String[] args) {
		int myInt = 88; //Integer 32 bit
                short myShort; //Short 16 bit
                long myLong; //Long 64 bit
                byte myByte; //Byte 8 bit

                double myDouble; //Double 
                float myFloat = 325.25f //Float
                
		char myChar = 'y'; //Char
                boolean myBoolean = true; //Boolean
	}

}

Strings

public class stringstuto {
	public static void main(String[] args) {
                int myInt = 7;
		String myString1 = "Hello ";
                String myString2 = "Rafa";
                String myString3 = myString1 + myString2;
                
                System.out.println(myString3);
                System.out.println("My integer is: " + myInt);
	}
}

Loops

While

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

For

for(int i=0; i<5;i++){
	System.out.printf("The value of i is %d\n", i);
}

Do While

public static void main(String[] args) {
	Scanner myScanner = new Scanner(System.in);
	int value = 0;
		
	do{
		System.out.println("Enter a number: ");
		value = myScanner.nextInt();
	}
	while(value != 5);
	System.out.println("5!");
}

Conditional

if

int value = 20;
		
if(value < 10){
	System.out.println("Value < 10");
}
else if(value >= 10 && value < 20){
	System.out.println("value >=10 and value < 20");
}
else {
	System.out.println("value >= 20");
}

switch case

switch(VariableIntOrString){
case "start":
	System.out.println("Machine started!");
	break;
	
case "stop":
	System.out.println("Machine stopped");
	break;

default:
	System.out.println("Command not recognized");
}

User Input

import java.util.Scanner;

public class UserInput {
	public static void main(String[] args) {
		Scanner myInput = new Scanner(System.in);
		
		System.out.println("Enter a line of text: ");
		String line = myInput.nextLine();
		System.out.println("You entered: " + line);

                System.out.println("Enter a number: ");
                int value = myInput.nextInt();
                System.out.println("You entered: " + value);

                System.out.println("Enter a number: ");
                double dvalue = myInput.nextDouble();
                System.out.println("You entered: " + dvalue);
	}
}

• Note: Ctrl + Shift + O in eclipse adds all the imports you need.

Arrays

int[] values;
values = new int[3];
int[] values2 = {5, 24, 12};
values[0] = 10;

values.length; → returns the array lenght

Iterating trough an array

String[] fruits = {"apple", "banana", "pear", "kiwi"};
for(String fruit: fruits){
        System.out.println(fruit);
}

Multidimensional arrays

int[][] grid = {
         {3, 5, 12},
         {2, 4},
         {25, 12, 0}
};
System.out.println(grid[1][1];
String[][] = new String[2][3];

Classes and Objects

class Person {
    String name;
    int age;
    
    void speak(String text) {
            System.out.println(text + name + " and i am " + age + " years old."); 
    }
    int yearsToRetire () {
            int yearsLeft = 67 - age;
            return yearsLeft;
    }
}

public class Classes {
    public static void main(String[] args){
            Person person1 = new Person();
            
            person1.name = "Joe Doe";
            person1.age = 37;

            person1.speak("My name is: ");
            System.out.println("Years to retirement= " + person1.yearsToRetire());
    }
}

Eclipse shortcuts

Ctrl + Space → Autocomplete.
Ctrl + d → Delete Line
Ctrl + o → Automatically add imports
Ctrl + Shift + f → Indent