Java Control Flow

Control flow statements are exactly what the term means. They are statements that alter execution flow based on decisions, loops and branching so that the program can conditionally execute blocks of code.

Primarily, Java has the following constructs for flow control:

  1. if…if( <expression that results in a boolean> ){ //code enters this block if the above expression is ‘true’ }
  2. if…else if( <expression that results in a boolean> ){ //execute this block if the expression is ‘true’ } else{ //execute this block if the expression is ‘false’ }
  3. switch

Switch statement

The switch statement is an alternative for the if...else construct when there are multiple values and cases to check against.

switch( <integer / String / Enum > ){ case <int/String/Enum>: <statements> break; case <int/String/Enum>: <statements> break; default: <statements> }

Note: The program flow falls through the next case if the break statement is missing. e.g. Let’s say you say the standard ‘Hello’ to everyone at office, but you are extra nice to the girl who sits next to you and sound grumpy to your boss. The way to represent would be something like:

switch(person){ case 'boss': soundGrumpy(); break; case 'neighbour': soundExtraNice(); break; case 'colleague': soundNormal(); break; default: soundNormal(); }

Note: The default case runs when none of the case matches. Remember that when a case has no break statement, it falls through to the next case and will continue to the subsequent cases till a break is encountered. Because of this, make sure that each case has a break statement. The default case does not require a break statement.

Nested statements

Any of the previous control flows can be nested. Which means you can have nested if, if..else and statements. i.e., you can have any combination of these statements within the other and there is no limitation to the depth ofnesting.

For example, let’s consider the following scenario:

  • If you have less than 25 bucks, you get yourself a cup of coffee.
  • If you have more than 25 bucks but less than 60 bucks, you get yourself a decent meal.
  • If you have more than 60 bucks but less than a 100, you get yourself a decent meal along with a glass of wine.
  • However, when you have more than a 100 bucks, depending on who you are with, you either go for a candle lit dinner (with your wife) or you go to a sports bar (with your friends).

One of the ways to represent this will be:

int cash = 150; String company = "friends"; if( cash < 25 ){ getCoffee(); } else if( cash < 60 ){ getDecentMeal(); } else if( cash < 100 ){ getDecentMeal(); getGlassOfWine(); } else { switch(company){ case "wife": candleLitDinner(); break; case "friends": meetFriendsAtSportsBar(); break; default: getDecentMeal(); } }

In this example, meetFriendsAtSportsBar() will be executed.

Ternary operator

The ternary operator is a nice alternative to simple if...else structures. It is an expression taking 3 operands that allows you to write in one line what you would otherwise have written in 4-6 lines. This expression returns a value, so it can be used in assignments or as a continionnal parameter when calling a function.

(condition) ? valueIfTrue : valueIfFalse
int number = 15; String s = number > 10 ? "high" : "low"; System.out.println(number > 10 ? "high" : "low");

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