---

Exam Objectives Covered

• Describe the looping statements


• Use a "for" loop including an enhanced "for" loop*


• Use a "while" loop


• Use a "do-while" loop


• Compare and contrast the "for," "while," and "do-while" loops


• Develop code that uses "break" and "continue" statements


• Use the decision-making statement (if-then and if-then-else)


• Use the "switch" statement

---

if Statement

• Braces not required


• Recommend always using braces

if (boolean-expr)
  // do an action

if (boolean-expr) {
  // do an action
  // do another action
}

// remember: = is assignment, == is comparison
if (x = 5) {   // ERROR: should be x == 5
  // do something
}

---

if-else Statement

if (boolean-expr) {
  // do an action
  // do another action
}
else {
  // do something else
}

public static void main(String[] args) {
  String str = (args.length == 1) ? "1" : "not 1";
}

• Compact alternative: ternary operator (3 operands)

boolean-expr ? true-value : false-value

• You can nest them

double pay(int hours, double rate) {

  double basePay = hours * rate;
  double multiplier = 0;  // why declare it here?
    
  if (hours > 50) {
    multiplier = 1.75;
  }
  else if (hours > 40) {
    multiplier = 1.5;
  }
  else {
    multiplier = 1;
  }
  return basePay * multiplier;
}

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Lab 6.1 - Even or Odd

• Create a class called "EvenOrOdd"
• Add a main method


• Declare an int called "myNumber" and assign it to a value of your choosing


• Inside of an if statement, evaluate whether "myNumber" is even using modulo and comparison
• HINT: This was covered in Section 4
• If true, print to the console, "myNumber is even!"


• Inside of an else statement, print to the console, "myNumber is odd!"


• Test your program with different values for "myNumber" to ensure that it functions correctly


• CHALLENGE: Use a ternary operator instead of an if-else statement

---

switch Statement

• Like if-else, but can make multiple choices


• Execution begins at the first case that matches the variable
• And continues until it reaches a break


• If no case matches, executes the default case (if present)

// NOTE: can only switch on int or smaller (byte, short, int, char) // as well as String and enums (more on enums later)
switch (variable) {
  case value1:
    // statements
    break;
  
  case value2:
    // statements
    break;
  
  default:
    // statements
}

---

switch Statement - Example

• Notice how the cases are used here

void determineRange(int i) {
  switch (i) {
    case 1: case 2: case 3:
      System.out.println("i is between 1 and 3");
      break;
    case 4: case 5: case 6:
      System.out.println("i is between 4 and 6");
      break;
    case 7: case 8: case 9:
      System.out.println("i is between 7 and 9");
      break;
    default:
      System.out.println("i is out of range");
  }
}

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Lab 6.2 - Daily Message

• Create a class called "DailyMessage"
• Add a main method


• Declare a String called "dayOfTheWeek" and assign the value to the day of the week today


• Create a switch statement that takes the "dayOfTheWeek" String as an argument
• Print "Class day" if the day of the week is Monday, Wednesday, or Friday
• Print "Gym day" if the day of the week is Tuesday or Thursday
• Print "Weekend" if the day of the week is Saturday or Sunday
• Remember that Java is case-sensitive!

---

while Loop

• Braces not required


• Recommend always using braces

while (boolean_expr)
  // do an action

while (boolean_expr) {
  // do an action
  // do another action
}

---

Lab 6.3 - Soda on the Wall 1

• Create a class called "SodaOnTheWall1"
• Add a main method


• Declare an int called "counter" and assign it to the value of 99


• Use a while loop and "counter" to print this song:

99 bottles of soda on the wall!
99 bottles of soda!
Take one down and pass it around,
98 bottles of soda on the wall!
[and so on…]

• If counter equals 0, print an alternative message:

No more bottles of soda on the wall,
no more bottles of soda!
Go to the store and buy some more,
99 bottles of soda on the wall!

• CHALLENGE: How could we get an infinite loop and continue the song correctly?

---

do-while Loop

• Braces not required


• Recommend always using braces


• Will always execute at least once


• Easy to miss that trailing semicolon

do 
  // do an action
while (boolean_expr);

do {
  // do an action
  // do another action
} while (boolean_expr);

---

Lab 6.4 - Soda on the Wall 2

• Create a class called "SodaOnTheWall2"
• Add a main method


• Rewrite the "SodaOnTheWall1" class but use a do-while loop instead of a while loop
• HINT: Copy and paste!


• Try running this version while counter is set to an initial value of -1
• Did it behave the way you expected?

---

for Loop

• Most commonly used loop in Java


• Initialization
• Sets initial values, can also include a variable


• Boolean expression
• Loop repeats until false


• Iteration/increment
• Fires just after body of the loop (just before the closing })
• Prior to the next test on the boolean_expr

for (initialization; boolean_expr; iteration) {
  // statements
}

---

for Loop - Examples

// i declared outside for block, because we need it later
int i;
for (i = 0; i < 5; i++) {
  System.out.println("i is now " + i);
}
...
System.out.println("i after for loop is " + i);  // i still in scope

// i is declared in the scope of the for block (typical case)
for (int i = 0; i < 5; i++) {
  System.out.println("i is now " + i);
}
// i is now out of scope (see notes)

---

for Loop - Multiple Initializations

• Initialization or iteration can have multiple expressions
• Use commas to separate

for (int s = 0, int t = 1; s + t < 30; s++, t+=3) {
  System.out.println("s is " + s + ", t is " + t);
}

s is 0, t is 1
s is 1, t is 4
s is 2, t is 7
s is 3, t is 10
s is 4, t is 13
s is 5, t is 16
s is 6, t is 19
s is 7, t is 22

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Lab 6.5 - Soda on the Wall 3

• Create a class called "SodaOnTheWall3"
• Add a main method


• Rewrite the "SodaOnTheWall1" class but use a for loop instead of a while loop
• HINT: Copy and paste!


• This version should have the least total lines of code
• Does yours? Why is this?

---

break and continue

• Alter the flow of a loop


• Often used for efficiency reasons
• If you're looping to search for a value, once you find it, stop looping


• Sometimes stand alone, sometimes used with labels


• break - stop executing loop entirely


• continue - stop current iteration and continue with the next

---

break - Example

class BreakOut {
  
  public static void main(String args[]) {
    int limit = 3;
    for (int j = 0; j < 5; j++) {
      if (j == limit)
        break;  // stop loop entirely
      System.out.println("j is " + j);
    }
  }
}

• What does this output?

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continue - Example

class ContinueOn {
  
  public static void main(String args[]) {
    int limit = 3;
    for (int j = 0; j < 5; j++) {
      if (j == limit)
        continue;  // stop current iteration and continue with next
      System.out.println("j is " + j);
    }
  }
}

• What does this output?