Logic

If statements

if statements are used to check the status of variables. The simplest way to do this is with booleans, because you can just use them by themselves. Other types require you to compare them in some way, so that the end result is true or false

if (boolean) {
    code; // Runs if boolean == true
} else {
    code; // Otherwise runs this
}

Here are some comparison operators:

• <, >: Less than, Greater than
• <=, >=: Less than or equal to, Greater than or equal to
• ==: Equivalent to
• !=: Not equivalent to
• !: Not (inverts any boolean after it, so true->false and vice-versa)
• &&: And (True: (1 == 1) && (2 == 2), checks if 1 is equal to 1 and 2 is equal to 2)
• ||: Or (True: (1 == 1) || (2 != 2), checks if 1 is equal to 1 or 2 is equal to 2)
• ^: Xor (True: (1 == 1) ^ (2 != 2), True if only one of the conditions is true)

Here are some examples:

// Reads like: "if one plus one equals two"
if (1 + 1 == 2) {
    System.out.println("Math is mathin'");
}

// Reads like: "if one does not equal two"
if (1 != 2) {
    System.out.println("Cool bro");
}

// Reads like: "if one plus one equals two and three plus three equals six"
if (1 + 1 == 2 && 3 + 3 == 6) {
    System.out.println("Math is still mathin'");
}

Variables can be used in if statements as well, as long as they are boolean’s.

boolean valid = 1 == 1;
if (valid) {
    System.out.println("1 == 1 Yay");
}

if (motorRunning && desiredMotorState == MotorState.kSTOP) {
    motor.Set(0);
    currentMotorState = MotorState.kSTOP;
}

if (elevator.atBottomHardStop() || elevator.atUpperHardStop()) {
    motor.Set(0);
    currentMotorState = MotorState.kSTOP;
}

A Addendum for Non-Primative Types (For Those Who Care)

Due to the way that java works, when you compare a non-primative type to anything else you are not comparing the value of the variable, but insted the address to the memory of the variable. Some of the consequences of this is that code like String("abc") == "abc" is false (String is a non primative type). For strings and others, you can do String("abc").equals("abc") to get it to work.

For loops

You can use loops to run code more than once without copy+pasting 800 lines. A straightforward way to do this is a for loop. for loops run a pre-specified amount of times, defined in the parentheses after for. A common syntax you will see is defining a new variable (often i), then setting a condition (while i is less than 5), and setting a rule to be followed every loop (commonly i++, which increments i by 1).

for (int i = 0; i < 5; i++) {
    code; // Runs 5 times
}

While loops

while loops run the code within their brackets, then check their condition (a boolean). If true, the loop runs again and the cycle repeats. These are not often seen in robot code because it is very easy to lock up an entire robot system with a while loop.

while (boolean) {
    code; // Runs until boolean == false
}

Switch statements

switch statements are like the cooler if statement. They compare a value to a series of cases, and use the matching case. The break; tells the compiler to stop reading code and exit the switch statement.

int which = 2;
switch (which) {
    case 0:
        code;
        break;
    case 1:
        code;
        break;
    case 2:
        code; // This code runs
        break;
    case 3:
        code;
        break;
}