Java Conditionals

If-Else Statements

If-Else statements are conditional statements that determine which section of code to run.

/*
 Example 1:
 If condition is not true, else is executed
 */

int x = 5; // variable x
if (x<4){ // the line of code within the if statement will not be executed as x is not less than 4
    System.out.println("X is less than 4");
}
else { // the line of code within the else statement is executed because first condition is not true
    System.out.println("X is greater than 4");
}

X is greater than 4

/*
 Example 2:
 If condition is true, else is not executed
 */

int x = 3; // variable x
if (x<4){ // the line of code within the if statement will be executed as x is less than 4
    System.out.println("X is less than 4");
}
else { // the line of code within the else statement is not executed because first condition is true
    System.out.println("X is greater than 4");
}

X is less than 4

If-Elseif-Else Statements

If-Elseif-Else statements are another conditional statement, this time with 3 different code segments to execute from. Both the if and elseif need a condition, while the else does not.

/*
 Example 3:
If condition false, else if condition true. Else if code is executed
 */

int x = 2; // variable x
if (x<4 && x>3 ){ // the line of code within the if statement will not be executed, as x is not between 3 and 4
    System.out.println("X is less than 4");
}
else if (x == 2){ // the line of code within the else if statement is executed as x is equal to 2
    System.out.println("X is equal to 2");
}
else { // the line of code within the else statement is not executed because the previous condition is true
    System.out.println("X is greater than 4");
}

X is equal to 2

Switch-case

There are many ways to write code. In the case of conditionals, a switch case can be used to replace a if-elseif-else statement. In a switch statement, one of many code blocks will be executed.

// this is an if-else-else statement
String cheese = "Gouda";
if (cheese == "Cheddar"){ // tests if cheese = cheddar
    System.out.println("Cheddar originated in Somerset");
}
else if (cheese == "Gouda"){ // tests if cheese = gouda
    System.out.println("Gouda originated in the Netherlands");
}
else if (cheese == "Milk"){ // tests if cheese = milk
    System.out.println("Milk is made from cows, goats, and other mammals");
}
else if (cheese == "Cheese"){ // tests if cheese = cheese
    System.out.println("Cheese is very yummy");
}
else{ // if cheese is none of these
    System.out.println("Sorry, I don't have any information about " + cheese);
}

Gouda originated in the Netherlands

//the statement above can also be written like:
String cheese = "Gouda";
switch(cheese) {
    case "Cheddar": // tests if cheese = cheddar
        System.out.println("Cheddar originated in Somerset");
        break;
    case "Gouda": // tests if cheese = gouda
        System.out.println("Gouda originated in the Netherlands");
        break;
    case "Milk": // tests if cheese = milk
        System.out.println("Milk is made from cows, goats, and other mammals");
        break;
    case "Cheese": // tests if cheese = cheese
        System.out.println("Cheese is very yummy");
    default: // if cheese is none of these
        System.out.println("Sorry, I don't have any information about " + cheese);   
}

Gouda originated in the Netherlands

De Morgan's Law

De Morgan's Law illustrates how compound boolean expressions are read. It helps you simplify code and your logic operators.

boolean a = true;
boolean b = false;

if (!(a && b)){
    System.out.println("!(true && false) is true");
}
else {
    System.out.println("!(true && false) is false");
}

!(true && false) is true