A list of all assignment operators: Operator Example Same As = x = 5 x = 5 += x += 3 x = x + 3 -= x -= 3 x = x - 3 *= x *= 3 x = x * 3 /= x /= 3 x = x / 3 %= x %= 3 x = x % 3 &= x &= 3 x = x & 3 |= x |= 3 x = x | 3 ^= x ^= 3 x = x ^ 3 >>= x >>= 3 x = x >> 3 <<= x <<= 3 x = x << 3 @BikramMaharjan
Java Comparison Operators Operator Name Example == Equal to x == y != Not equal x != y > Greater than x > y < Less than x < y >= Greater than or equal to x >= y <= Less than or equal to x <= y @BikramMaharjan
Java Logical Operators Operator Name Description Example && Logical and Returns true if both statements are true x < 5 && x < 10 || Logical or Returns true if one of the statements is true x < 5 || x < 4 ! Logical not Reverse the result, returns false if the result is true !(x < 5 && x < 10) @BikramMaharjan
Example(Logical &&) public class Main { public static void main(String[] args) { int x = 5; System.out.println(x > 3 && x < 10); // returns true because 5 is greater than 3 AND 5 is less than 10 } } @BikramMaharjan
Example(Logical ||) public class Main { public static void main(String[] args) { int x = 5; System.out.println(x > 3 || x < 4); // returns true because one of the conditions are true (5 is greater than 3, but 5 is not less than 4) } } @BikramMaharjan
Example(Logical !) public class Main { public static void main(String[] args) { int x = 5; System.out.println(!(x > 3 && x < 10)); // returns false because ! (not) is used to reverse the result } } @BikramMaharjan
Activity System.out.println(10 5); @BikramMaharjan
Java Strings Strings are used for storing text. A String variable contains a collection of characters surrounded by double quotes: public class Main { public static void main(String[] args) { String greeting = "Hello"; System.out.println(greeting); } } @BikramMaharjan
String Length A String in Java is actually an object, which contain methods that can perform certain operations on strings. For example, the length of a string can be found with the length() method: public class Main { public static void main(String[] args) { String txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; System.out.println("The length of the txt string is: " + txt.length()); } } @BikramMaharjan
String Uppercase and lowercase Method public class Main { public static void main(String[] args) { String txt = "Hello World"; System.out.println(txt.toUpperCase()); System.out.println(txt.toLowerCase()); } } @BikramMaharjan
Finding a Character in a String public class Main { public static void main(String[] args) { String txt = "Please locate where 'locate' occurs!"; System.out.println(txt.indexOf("locate")); } } @BikramMaharjan
String Concatenation public class Main { public static void main(String args[]) { String firstName = "John"; String lastName = "Doe"; System.out.println(firstName + " " + lastName); } } @BikramMaharjan
String (Concat() method) public class Main { public static void main(String[] args) { String firstName = "John "; String lastName = "Doe"; System.out.println(firstName.concat(lastName)); } } @BikramMaharjan
Activity Fill in the missing part to create a greeting variable of type String and assign it the value Hello. greeting = ; @BikramMaharjan
Java Math (Math.max(x,y)) The Math.max(x,y) method can be used to find the highest value of x and y: public class Main { public static void main(String[] args) { System.out.println(Math.max(5, 10)); } } @BikramMaharjan
Math.min(x,y) The Math.min(x,y) method can be used to find the lowest value of x and y: public class Main { public static void main(String[] args) { System.out.println(Math.min(5, 10)); } } @BikramMaharjan
Math.sqrt(x) The Math.sqrt(x) method returns the square root of x: public class Main { public static void main(String[] args) { System.out.println(Math.sqrt(64)); } } @BikramMaharjan
Java Conditions and If Statements Java supports the usual logical conditions from mathematics: Less than: a < b Less than or equal to: a <= b Greater than: a > b Greater than or equal to: a >= b Equal to a == b Not Equal to: a != b @BikramMaharjan
Java Conditions and If Statements Java has the following conditional statements: • Use if to specify a block of code to be executed, if a specified condition is true • Use else to specify a block of code to be executed, if the same condition is false • Use else if to specify a new condition to test, if the first condition is false • Use switch to specify many alternative blocks of code to be executed @BikramMaharjan
The if Statement public class Main { public static void main(String[] args) { int x = 20; int y = 18; if (x > y) { System.out.println("x is greater than y"); } } } @BikramMaharjan
The else Statement public class Main { public static void main(String[] args) { int time = 20; if (time < 18) { System.out.println("Good day."); } else { System.out.println("Good evening."); } } } @BikramMaharjan
The else if Statement public class Main { public static void main(String[] args) { int time = 22; if (time < 10) { System.out.println("Good morning."); } else if (time < 20) { System.out.println("Good day."); } else { System.out.println("Good evening."); } } } @BikramMaharjan
Java Switch Statements switch(expression) { case x: // code block break; case y: // code block break; default: // code block } @BikramMaharjan
Switch Case Example public class Main { public static void main(String[] args) { int day = 4; switch (day) { case 1: System.out.println("Monday"); break; case 2: System.out.println("Tuesday"); break; case 3: System.out.println("Wednesday"); break; case 4: System.out.println("Thursday"); break; case 5: System.out.println("Friday"); break; case 6: System.out.println("Saturday"); break; case 7: System.out.println("Sunday"); break; } } } @BikramMaharjan
Loops Loops can execute a block of code as long as a specified condition is reached. Loops are handy because they save time, reduce errors, and they make code more readable. 1. While loop 2. Do while loop 3. For loop @BikramMaharjan
Java While Loop The while loop loops through a block of code as long as a specified condition is true: while (condition) { // code block to be executed } @BikramMaharjan
EXAMPLE public class Main { public static void main(String[] args) { int i = 0; while (i < 5) { System.out.println(i); i++; } } } @BikramMaharjan
Java For Loop When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop: for (statement 1; statement 2; statement 3) { // code block to be executed } @BikramMaharjan
EXAMPLE public class Main { public static void main(String[] args) { for (int i = 0; i < 5; i++) { System.out.println(i); } } } @BikramMaharjan
The Do/While Loop The do/while loop is a variant of the while loop. This loop will execute the code block once, before checking if the condition is true, then it will repeat the loop as long as the condition is true. do { // code block to be executed } while (condition); @BikramMaharjan
EXAMPLE public class Main { public static void main(String[] args) { int i = 0; do { System.out.println(i); i++; } while (i < 5); } } @BikramMaharjan
Java Arrays Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value. To declare an array, define the variable type with square brackets: String[] cars; String[] cars = {"Volvo", "BMW", "Ford", "Mazda"}; To create an array of integers, you could write: int[] myNum = {10, 20, 30, 40}; @BikramMaharjan
Access the Elements of an Array public class Main { public static void main(String[] args) { String[] cars = {"Volvo", "BMW", "Ford", "Mazda"}; System.out.println(cars[0]); } } You access an array element by referring to the index number. This statement accesses the value of the first element in cars: @BikramMaharjan
Change an Array Element To change the value of a specific element, refer to the index number: public class Main { public static void main(String[] args) { String[] cars = {"Volvo", "BMW", "Ford", "Mazda"}; cars[0] = "Opel"; System.out.println(cars[0]); } } @BikramMaharjan
Array Length To find out how many elements an array has, use the length property: public class Main { public static void main(String[] args) { String[] cars = {"Volvo", "BMW", "Ford", "Mazda"}; System.out.println(cars.length); } } @BikramMaharjan
ACTIVITY Create an array of type String called cars. = {"Volvo", "BMW", "Ford"}; @BikramMaharjan
Java Arrays Loop Loop Through an Array You can loop through the array elements with the for loop, and use the length property to specify how many times the loop should run. The following example outputs all elements in the cars array: @BikramMaharjan
Loop Through an Array public class Main { public static void main(String[] args) { String[] cars = {"Volvo", "BMW", "Ford", "Mazda"}; for (int i = 0; i < cars.length; i++) { System.out.println(cars[i]); } } } @BikramMaharjan
Loop Through an Array with For-Each There is also a "for-each" loop, which is used exclusively to loop through elements in arrays: Syntax: for (type variable : arrayname) { ... } @BikramMaharjan
For each loop example public class Main { public static void main(String[] args) { String[] cars = {"Volvo", "BMW", "Ford", "Mazda"}; for (String i : cars) { System.out.println(i); } } } @BikramMaharjan
Java Methods A method is a block of code which only runs when it is called. You can pass data, known as parameters, into a method. Methods are used to perform certain actions, and they are also known as functions. Why use methods? To reuse code: define the code once, and use it many times. @BikramMaharjan
Create a Method A method must be declared within a class. It is defined with the name of the method, followed by parentheses (). Java provides some pre-defined methods, such as System.out.println(), but you can also create your own methods to perform certain actions: public class Main { static void myMethod() { // code to be executed } } @BikramMaharjan
Example Explained • myMethod() is the name of the method • static means that the method belongs to the Main class and not an object of the Main class. You will learn more about objects and how to access methods through objects later in this tutorial. • void means that this method does not have a return value. You will learn more about return values later in this chapter @BikramMaharjan
Call a Method To call a method in Java, write the method's name followed by two parentheses () and a semicolon; In the following example, myMethod() is used to print a text (the action), when it is called: @BikramMaharjan
Example (calling a method) public class Main { static void myMethod() { System.out.println("I just got executed!"); } public static void main(String[] args) { myMethod(); } } @BikramMaharjan
A method can also be called multiple times: public class Main { static void myMethod() { System.out.println("I just got executed!"); } public static void main(String[] args) { myMethod(); myMethod(); myMethod(); } } @BikramMaharjan
Activity Insert the missing part to call myMethod from main. static void myMethod() { System.out.println("I just got executed!"); } public static void main(String[] args) { ; } @BikramMaharjan
Java Method Parameters Parameters and Arguments Information can be passed to methods as parameter. Parameters act as variables inside the method. Parameters are specified after the method name, inside the parentheses. You can add as many parameters as you want, just separate them with a comma. @BikramMaharjan
Java Method Parameters The following example has a method that takes a String called fname as parameter. When the method is called, we pass along a first name, which is used inside the method to print the full name: public class Main { static void myMethod(String fname) { System.out.println(fname + " Verma"); } public static void main(String[] args) { myMethod(“Anjali"); myMethod(“Sumit"); myMethod(“Kavita"); } } @BikramMaharjan
Java - What is OOP? OOP stands for Object-Oriented Programming. Procedural programming is about writing procedures or methods that perform operations on the data, while object-oriented programming is about creating objects that contain both data and methods. Object-oriented programming has several advantages over procedural programming: • OOP is faster and easier to execute • OOP provides a clear structure for the programs • OOP helps to keep the Java code DRY "Don't Repeat Yourself", and makes the code easier to maintain, modify and debug • OOP makes it possible to create full reusable applications with less code and shorter development time @BikramMaharjan