Branching

• Processing can rarely be done by a single list of instructions.
• We usually need to have different sets of code running, depending on conditions or user interaction.
• For this, we need to branch our code down one or more execution paths.

If

• The simplest form is the if-statement:

  if (some condition) { 
      do something; 
  }
  

• For example:

  if (earthRadius == 6378) {	
      System.out.print("radius correct");
  }
  

• Block only done if the whole condition is true.
• Note that if there's only one line, it can be written without brackets, but avoid this.

if... else...

• The if-else statement lets us branch down two mutually exclusive routes:

• if (condition) {do something;} 
  else {do something else;}
  

• For example:

  if (earthRadius == 6378) {	
      System.out.println("radius correct");
  } else {
      earthRadius = 6378;
      System.out.println("radius corrected");
  }
  

Ternary kung fu

• The ?: Ternary operator
  • A replacement for the if / else statement in assignment.
  • The most nifty move you can pull. Use it and other coders will give you a knowing nod in the street. You will be the Jackie Chan Kung Fu King/Queen of Code.
• How do I pull this amazing move?

  variable = condition?expression1:expression2;
  

  If the condition is true, expression1 is used, otherwise expression2 is used.

Ternary example

name = (fileFound==true)?(filename):(defaultName);

if (fileFound==true) {
    name = filename;
} else {
    name = defaultName;
}

• Why use it?
  Because we can... just because we can.

if / else / if ladder

if (condition) 
    statement or {statements;}
else if (condition) 
    statement or {statements;}
else if (condition) 
    statement or {statements;}
else
    statement or {statements;}

Switch

switch (variable) {
    case value1:
		statements1;
		break;
    case value2:
		statements2;
		break;
    case value3:
		statements3;
		break;
    default:
		statements4;
}

• Slightly slower, but not as slow as a bad if-else-if ladder.
• The break's are optional, if you leave one out, the computer will just run on into the next values case statements.

int day = 7;

switch (day) {
    case 6:
		System.out.println("Saturday");
		break;
    case 7: 
		System.out.println("Sunday");
		break;
    default: 
		System.out.println("Meh, whatever");
}

Review

if (some condition) { 
    do something; 
} else {
    do something else; 
}