Session Three Review & Conditional Control Flow

Java File Hierarchy Projects Packages Classes Methods

Variables Everything is case-sensitive 2 types Primitive (int, float, double) Non-primitive (String) 3 parts Type Name Value int num = 5;

Variable Assignment Every variable must has some value in order to use it Initialization is the first assignment Try to initialize it when you declare it int num = 5; int num; num = 5; Both of these are equally valid Declaration First Assignment (aka Initialization)

Variable Assignment Can only assign a variable it’s type of data Sometimes Java automatically converts stuff You can do it manually if you need to String str = 5; //wrong String str = “5”; //correct int num = “5”; //wrong int num = 5; //correct

New Stuff: Conditional Control Flow The program changes what it does depending on some condition if statements int num = 5; if (num > 10) { //skips this code } //continues here int num = 5; if (num < 10) { //runs this code } //continues here

Relational Operators What you use to compare two things OperatorUse a == bEqual to a != bNot equal to a > bGreater than a >= bGreater than or equal to a < bLess than a <= bLess than or equal to

Relational Operators Now write a program that uses all of these OperatorUse a == bEqual to a != bNot equal to a > bGreater than a >= bGreater than or equal to a < bLess than a <= bLess than or equal to public static void main(String[] args){ int a = 5; int b = 5; if (a == b) { System.out.println(“==”); } // other if statements here }

Conditional Control Flow if… else statements “else” does stuff if the condition is false if (condition) { //condition is true } else { //condition is false } //continues here

boolean Primitive Type boolean variables store either true or false Can be used in conditional control flow boolean logic = true; if (logic) { System.out.println(“logic is true.”); }

Logical Operators Used with boolean value types ! – logical NOT inverts boolean values && - logical AND true if both are true || - logical OR true if one is true !true == false !false == true true && false == false true || false == true

Logical Operators b1b2b1 && b2 false truefalse truefalse true b1b2b1 || b2 false true falsetrue Make 3 int variables: a, b, and c. If c is between a and b, print out “Yes.” If not, print out “No.” if (condition) { //condition is true } else { //condition is false }

if (a < b) { if (c a) { System.out.println("Yes.”); } else { System.out.println("No."); } } else { if (c b) { System.out.println("Yes."); } else { System.out.println("No."); }

Conditional Control Flow “else if” statements A way to chain multiple if statements It will execute the block of the first true condition Everything continues at the end if (condition1) { //condition1 is true } else if (condition2) { //condition2 is true } else if (condition3) { //condition3 is true } else { //all conditions are false } //everything continues here

What’s the difference? int a = 5; int b = 5; if (a == b) { System.out.println("a==b"); } else if (a >= b) { System.out.println("a>=b"); } int a = 5; int b = 5; if (a == b) { System.out.println("a==b"); } if (a >= b) { System.out.println("a>=b"); }

What’s the difference? int a = 5; int b = 5; if (a == b) { System.out.println("a==b"); } else if (a >= b) { System.out.println("a>=b"); } // prints out only "a==b" // remember, else if statements won’t // be checked if a previous condition // was true. int a = 5; int b = 5; if (a == b) { System.out.println("a==b"); } if (a >= b) { System.out.println("a>=b"); } // prints out "a==b" and "a>=b"

While Loops Executes a block of code over and over again until a condition is false while (condition) { //run this code } //continues here

While Loops Example This prints out numbers 1 – 10 Once num == 11, the condition is false, and it continues at the end of the block int num = 1; while (num <= 10) { System.out.println(num); num = num + 1; } //continues here

Caution With Using Loops It’s easy to get a program stuck in an infinite loop int num = 1; while (num <= 10) { System.out.println(num); } // won’t ever get here

End Mess around with Java, practice makes perfect This PowerPoint will be available online