Learning Java

Operators

Operators in Java are special symbols that perform specific operations on one, two or three operands and then return a result.

What is an Operand?

An operand is a term used to describe any object that is manipulated by an operator. If we consider below statement:

int myVar = 15 + 12;

Then + is the operator, and 15 and 12 are operands. Variables used instead of literals are also operands.

double mySalary = hoursWorked * hourlyRate;

In the above line hoursWorked and hourlyRate are operands, and * (multiplication) is the operator.

What is an Expression?

An expression is formed by combining variables, literals, method and return values and operators.

In the line below, 15 + 12 is the expression which has (or returns) 27 in this case.

int myVar = 15 + 12;

Summary:

What is a Comment?

Comments '//' are ignored by the computer and are added to a program to help describe something. Comments are there for humans. Aside from describing something about a program, comments can be used to temporarily disable code.

if-then Statements in Java

The if-then statement is the most basic of all control flow statements. It tells the program to execute a certain section of code only if a particular test evaluates to true. This is known as conditional logic.

Conditional Logic

Conditional logic uses specific statements in Java to allow us to check a condition and execute certain code based on whether that condition (the expression) is true or false.

	boolean isAlien = false;
	if (isAlien == true)// toggle the value to true/false to see the output
		System.out.println("It is not an Alien.");
		System.out.println("And I'm scared of Alien.");

		

	boolean isAliens = false;
	if (isAliens == false) {// toggle the value to true/false to see the output
		System.out.println("It is not an Alien.");
		System.out.println("And I'm scared of Alien.");
	}	
		

Java Operator Precedence Table

Larger number means higher precedence. Link

Summary of Operators:

Simple Assignment Operator

=       Simple assignment operator

Arithmetic Operators

+       Additive operator (also used
        for String concatenation)
-       Subtraction operator
*       Multiplication operator
/       Division operator
%       Remainder operator

Unary Operators

+       Unary plus operator; indicates
        positive value (numbers are 
        positive without this, however)
-       Unary minus operator; negates
        an expression
++      Increment operator; increments
        a value by 1
--      Decrement operator; decrements
        a value by 1
!       Logical complement operator;
        inverts the value of a boolean

Equality and Relational Operators

==      Equal to
!=      Not equal to
>       Greater than
>=      Greater than or equal to
<       Less than
<=      Less than or equal to

Conditional Operators

&&      Conditional-AND
||      Conditional-OR
?:      Ternary (shorthand for 
        if-then-else statement)

Type Comparison Operator

instanceof      Compares an object to 
                a specified type 

Bitwise and Bit Shift Operators

~       Unary bitwise complement
<<      Signed left shift
>>      Signed right shift
>>>     Unsigned right shift
&       Bitwise AND
^       Bitwise exclusive OR
|       Bitwise inclusive OR

Operator Examples:

	//result = result + 1;
	
	result++; // 1 + 1
	System.out.println("1 + 1 = "+result);
		
	result--;
	System.out.println("2 - 1 = "+result);
		
	// result = result + 2;
	result += 2;
	System.out.println("1 + 2 = "+result);

	// result = result * 10;
	result *= 10;
	System.out.println("3 * 10 = "+result);
		
	// result = result / 10;
	result /= 10;
	System.out.println("30 / 10 = "+result);
		
	// result = result - 2;
	result -= 2;
	System.out.println("3 - 2 = "+result);

	int secondTopScore = 60;
	if (topScore > secondTopScore && topScore < 100 ) {
		System.out.println("Greater than 2nd topscore and less than 100");
	}

	int topScore = 80;
	if (topScore != 100) { //toggle between "==" and "!=" to see the changes
		System.out.println("You got the high score!");
	}
		
	int topScore1 = 100;
	if (topScore1 <= 100) { //toggle between ">", "<", "<=" and ">=" to see the changes
		System.out.println("You got the high score!");
	}
		
	int secondTopScore = 60;
	if (topScore > secondTopScore && topScore < 100 ) {
		System.out.println("Greater than 2nd topscore and less than 100");
	}
		
	if ((topScore > 90) || (secondTopScore <= 90)) {
		System.out.println("Either or both of the conditions are true.");
	}

    isCar = true;
	boolean wasCar = isCar ? true : false;
	if (wasCar) {
		System.out.println("wasCar is true");
	}

Coding Examples:

	int newValue = 50;
	if (newValue = 50) { // this statement is expecting an int value, but considering it as boolean.
	// because with 'if' is used for a condition either 'yes' or 'no'.
	//here we're using assignment operator not equal operator hence the error.
		System.out.println("This is an error");
	}

	boolean isCar = false;
	if (isCar == true) { // this is not showing any error b/c we are already using the
	//expected type which is boolean. But this is logically not correct.
		System.out.println("This is not supposed to happen");
	}

		
	boolean isbike = false;
	if (isbike == true) { 
		System.out.println("This is not supposed to happen");
	} // Now no output as expected

	boolean iscycle = false;
	if (iscycle) { //by default considered true
		System.out.println("This is not supposed to happen");
	}

		
	boolean isbird = false;
	if (!isbird) {
		System.out.println("This is not supposed to happen bird");
	}

		
	boolean isbird = false;
	if (isbird == false) {
		System.out.println("This is not supposed to happen bird");
	}

		
	boolean isbird = false;
	if (isbird != true) {
		System.out.println("This is not supposed to happen bird");
	}

Operator Precedence & Operator Challenge

* 1. Create a double variable with a value of 20.00.
* 2. Create a second variable of type double with the value 80.00.
* 3. Add both numbers together and multiply by 100.00.
* 4. Use the remainder operator to figure out what the remainder from the result of * the operation in step 3 and 40.00.
* We used the modulus or remainder operator on ints, but we can also use it on double.
* 5. Create a boolean variable that assigns the value true if the remainder( %) in #4 is 0, * of false if it is not zero.
* 6. Output the boolean variable.
* 7. Write an 'if-then' statement that displays a message "Got some remainder" if the boolean * in #5 is not true.


package challanges;

public class OperatorsChallange {

	public static void main(String[] args) {
		
		double firstValue = 20.00d;
		double secondVariable = 80.00d;
		double operation = (firstValue + secondVariable) * 100.00d; 
		//if not using parenthesis, then operator precedence will follow
		System.out.println(operation);
		double remainder = operation % 40.00d;
		System.out.println(remainder);
		boolean output = (remainder == 0) ? true : false; ///// HIGHLIGHTED pay attention
		System.out.println(output);
		if (!output) {
			System.out.println("Got Some Remainder!!!");
		}
		/*
		 * if(remainder == 0) { output = true; }
		 * else { output = false; } 
		 * boolean finalOutput = output? true : false;
		 * if (!finalOutput) { System.out.println("Got Some Remainder!!!"); }
		 */
	}

}

Links: