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Java Switch

Java Switch Statements

Instead of writing many if..else statements, you can use the switch statement.

The switch statement selects one of many code blocks to be executed:

Syntax

switch(

expression

) {
  case x:
    // code block
    break;
  case y:
    // code block
    break;
  default:
    // code block
}

This is how it works:

The switch expression is evaluated once.
The value of the expression is compared with the values of each case.
If there is a match, the associated block of code is executed.
The break and default keywords are optional, and will be described later in this chapter

The example below uses the weekday number to calculate the weekday name: Continue reading Java Switch

Java If … Else Examples

Real-Life Examples

This example shows how you can use if..else to “open a door” if the user enters the correct code:

Example

int doorCode = 1337;

if (doorCode == 1337) {
  System.out.println("Correct code. The door is now open.");
} else {
  System.out.println("Wrong code. The door remains closed.");
}

This example shows how you can use if..else to find out if a number is positive or negative: Continue reading Java If … Else Examples

Java Short Hand If…Else (Ternary Operator)

Short Hand if…else

There is also a short-hand if else, which is known as the ternary operator because it consists of three operands.

It can be used to replace multiple lines of code with a single line, and is most often used to replace simple if else statements: Continue reading Java Short Hand If…Else (Ternary Operator)

Java Else If

The else if Statement

Use the else if statement to specify a new condition if the first condition is false.

Syntax

if (

condition1

) {
  // block of code to be executed if condition1 is true
} else if (

condition2

) {
  // block of code to be executed if the condition1 is false and condition2 is true
} else {
  // block of code to be executed if the condition1 is false and condition2 is false
}

Example

int time = 22;
if (time < 10) {
  System.out.println("Good morning.");
} else if (time < 18) {
  System.out.println("Good day.");
} else {
  System.out.println("Good evening.");
}
// Outputs "Good evening."

Continue reading Java Else If

Java Else

The else Statement

Use the else statement to specify a block of code to be executed if the condition is false.

Syntax

if (

condition

) {
  // block of code to be executed if the condition is true
} else {
  // block of code to be executed if the condition is false
}

Java If … Else

Java Conditions and If Statements

You already know that 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

You can use these conditions to perform different actions for different decisions.

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

Continue reading Java If … Else

Java Booleans

Very often, in programming, you will need a data type that can only have one of two values, like:

YES / NO
ON / OFF
TRUE / FALSE

For this, Java has a boolean data type, which can store true or false values.

Continue reading Java Booleans

Java Math

The Java Math class has many methods that allows you to perform mathematical tasks on numbers.

Math.max(x,y)

The Math.max(x,y) method can be used to find the highest value of x and y:

Example

Math.max(5, 10);

Continue reading Java Math

Java Special Characters

Strings – Special Characters

Because strings must be written within quotes, Java will misunderstand this string, and generate an error:

String txt = "We are the so-called "Vikings" from the north.";

The solution to avoid this problem, is to use the backslash escape character. Continue reading Java Special Characters

Java Numbers and Strings

Adding Numbers and Strings

WARNING!

Java uses the + operator for both addition and concatenation.

Numbers are added. Strings are concatenated.

If you add two numbers, the result will be a number:

Example

int x = 10;
int y = 20;
int z = x + y;  // z will be 30 (an integer/number)

If you add two strings, the result will be a string concatenation : Continue reading Java Numbers and Strings