Cars, Assemble!

Numbers

There are two different types of numbers in Java:

• Integers: numbers with no digits behind the decimal separator (whole numbers). Examples are -6, 0, 1, 25, 976 and -500000.
• Floating-point numbers: numbers with zero or more digits behind the decimal separator. Examples are -20.4, 0.1, 2.72, 16.984025 and 1024.0.

The two most common numeric types in Java are int and double. An int is a 32-bit integer and a double is a 64-bit floating-point number.

Arithmetic is done using the standard arithmetic operators. Numbers can be compared using the standard numeric comparison operators (eg. 5 > 4 and 4 <= 5) and the equality (==) and inequality (!=) operators.

Java has two types of numeric conversions:

1. Implicit conversions: no data will be lost and no additional syntax is required.
2. Explicit conversions: data could be lost and additional syntax in the form of a cast is required.

As an int has less precision than a double, converting from an int to a double is safe and is thus an implicit conversion. However, converting from a double to an int could mean losing data, so that requires an explicit conversion.

If-Else Statements

The if-then statement

The most basic control flow statement in Java is the if-then statement. This statement is used to only execute a section of code if a particular condition is true. An if-then statement is defined using the if clause:

class Car {
    void drive() {
        // the "if" clause: the car needs to have fuel left to drive
        if (fuel > 0) {
            // the "then" clause: the car drives, consuming fuel
            fuel--;
        }
    }
}

In the above example, if the car is out of fuel, calling the Car.drive method will do nothing.

The if-then-else statement

The if-then-else statement provides an alternative path of execution for when the condition in the if clause evaluates to false. This alternative path of execution follows an if clause and is defined using the else clause:

class Car {
    void drive() {
        if (fuel > 0) {
            fuel--;
        } else {
            stop();
        }
    }
}

In the above example, if the car is out of fuel, calling the Car.drive method will call another method to stop the car.

The if-then-else statement also supports multiple conditions by using the else if clause:

class Car {
    void drive() {
        if (fuel > 5) {
            fuel--;
        } else if (fuel > 0) {
            turnOnFuelLight();
            fuel--;
        } else {
            stop();
        }
    }
}

In the above example, driving the car when the fuel is less then or equal to 5 will drive the car, but it will turn on the fuel light. When the fuel reaches 0, the car will stop driving.