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EX2: WK5 Object Oriented Programming

Terms in this set (24)

Loop
A structure that allows repeated execution of a block of statements
Loop body
- A block of statements - Executed repeatedly
Iteration
- One execution of any loop
Definite or Counted loop
- Loop that executes specific number of times
Indefinite loop
- Loop executes undetermined number of times
while loop
■ The loop-controlling Boolean expression is the first statement

- Executes a body of statements continually ■ As long as the Boolean expression that controls entry into the loop continues to be true - Consists of: ■ The keyword X ■ Followed by a Boolean expression within parentheses ■ Followed by the body of the loop; can be a single statement or a block of statements surrounded by curly braces
do...while loop
■ The loop-controlling Boolean expression is the last statement
■ Loop will execute at least once
Definite loop
- Performs a task a predetermined number of times - Also called a counted loop
Infinite loop
- A loop that never ends - Can result from a mistake in the while loop - Do not write intentionally

Suspect an X when: - The same output is displayed repeatedly - The screen remains idle for an extended period of time
Accumulating
- Repeatedly increasing a value by some amount
+=
-=
*=
/=
%=
add and assign operator
subtract and assign operator
multiply and assign operator
divide and assign operator
remainder and assign operator
Prefix increment operator
++someValue

■ The result is calculated and stored ■ Then the variable is used

- Use only with variables - Unary operators ■ Use with one value - Increase a variable's value by 1 ■ No difference between operators (unless other operations are in the same expression)
postfix increment operator
someValue++

■ The variable is used ■ Then the result is calculated and stored

- Use only with variables - Unary operators ■ Use with one value - Increase a variable's value by 1 ■ No difference between operators (unless other operations are in the same expression)
for loop
■ A concise format in which to execute loops -Used when a definitenumber of loop iterations is required - One convenient statement indicates: ■ The starting value for the loop control variable ■ The test condition that controls loop entry ■ The expression that alters the loop control variable
Creating a for Loop
■ Other uses for the three sections of a X - Initialization of more than one variable ■ Place commas between separate statements - Performance of more than one test using AND or OR operators - Decrementing or performance of some other task - Altering more than one value ■ You can leave one or more portions of a X empty ■ Two semicolons are still required as placeholders ■ Use the same loop control variable in all three parts of a for statement ■ To pause a program: - Use the X that contains no body (do-nothingloop) for(x = 0; x < 100000; ++x); - Or use the built-in sleep() method
do...while loop
- A posttest loop - Checks the value of the loop control variable ■ At the bottom of the loop ■ After one repetition has occurred - Performs a task at least one time - You are never required to use this type of loop - Use curly braces to block the statement ■ Even with a single statement
Inner loop
An X must be entirely contained in an outer loop - Loops can never overlap
Outer loop
An inner loop must be entirely contained in an X - Loops can never overlap
Improving Loop Performance
■ Make sure a loop does not include unnecessary operations or statements - While(x < a+b) ■ Consider the order of evaluation for short-circuit operators - AND & OR uses short circuit expressions While(requestedNum > LIMIT || requestedNum <0) ■ Make comparisons to zero (0) - for(int x = 0; x <= REPEAT; ++x) vs. for(int x = REPEAT; x >= 0; --x) ■ Employ loop fusion to combine loops - A technique of combining two loops into one - Will not work in every situation - Improve performance if two methods does not depend on each other
Comparing to Zero
Making a comparison to X is faster than making a comparison to any other value ■ To improve loop performance, compare the loop control variable to X
Arrays
■ An X is a list of contiguous values in computer memory ■ An X has a specified size and does not change ■ Each item in an X is called an element ■ Each element in the X have the same data type ■ Each element can be accessed using a subscript ■ The subscript values are 0 to one number less than the size of the X
Initializing an Array 1/3
■ Array names: - Represent computer memory addresses - Contain references ■ When you declare an array name: - No computer memory address is assigned - The array has the special value null ■ Unicode value '\u0000'
Initializing an Array 2/3
■ Use the keyword new to define an array - The array name acquires the actual memory address value ■ int[] someNums = new int[10];
- Each element of someNums has a value of 0 ■ char array elements - Assigned '\u0000' ■ boolean array elements - Automatically assigned the value false ■ Strings and arrays of objects - Assigned null by default
Initializing an Array 3/3
■ Assign nondefault values to array elements upon creation int[] tenMult = {10, 20, 30, 40, 50, 60}; ■ An initialization list initializes an array - Values are separated by commas and enclosed within curly braces ■ Populating an array - Providing values for all the elements in an array ■ You can use the for loop to assign values to an array ■ In java, you cannot directly initialize part of an array - if there are 5 elements, you have initialize all 5 elements or no elements
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