AP Computer Science A Unit 3
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Last updated 10:44 PM on 11/21/25
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87 Terms
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Repetition
A form of iteration
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Control
Iteration statements change the flow of this by repeating a segment of code zero or more times
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True
What the boolean expression controlling the loop must evaluate to in order to repeat the segment of code
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One
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What is iteration?
Repetition of code controlled by a Boolean expression.
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When does a while loop check its condition?
Before executing the loop body.
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What causes infinite loops?
Condition never becomes false.
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What is an off-by-one error?
Loop runs one time too many or too few.
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3 parts of a for-loop header?
Initialization, condition, update.
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How many times is initialization executed in a for-loop?
Once before first check.
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When is the update executed?
After each loop body execution.
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Can loop control variable be used outside loop?
Only if declared before loop header.
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Convert for-loop to while-loop?
Move init before, condition in while, update inside.
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What is a nested loop?
A loop inside another; inner runs fully each outer iteration.
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How to compute total iterations of nested loops?
Outer count × inner count.
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Math.random() returns?
Double in [0.0,1.0).
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How to generate int in [a,b]?
(int)(Math.random()*(b-a+1))+a
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Import for File class?
import java.io.File;
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What must be added to main when using File?
throws IOException
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What happens if file name invalid?
FileNotFoundException.
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Construct File object?
File f = new File("data.txt");
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Construct Scanner for file?
Scanner input = new Scanner(f);
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What does hasNext() do?
Checks if more tokens exist.
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Difference: hasNextInt() vs nextInt()
hasNextInt checks, nextInt consumes.
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Why loop for input validation?
To repeatedly prompt until correct type.
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What does validation loop on p14 do?
Repeats until integer is entered.
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What to print on invalid input?
Error message; consume token with next().
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What does while(true) mean?
Creates an intentional infinite loop until a break occurs.
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When should you use a while loop?
When number of iterations is unknown beforehand.
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When should you use a for loop?
When number of iterations is known or count-controlled.
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What does break do?
Immediately exits the nearest loop.
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What does continue do?
Skips rest of loop body and proceeds to next iteration.
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Common cause of logic errors in loops?
Incorrect condition, update, or variable scope.
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What is loop accumulation?
Repeatedly updating a total inside a loop.
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Why initialize sum to 0?
So accumulation starts with a neutral element.
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Why initialize product to 1?
1 is the multiplicative identity.
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What is integer division used for?
Truncating decimal results when dividing ints.
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What is casting?
Forcing a value to another type, e.g., (double) num.
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Why cast when computing averages?
To avoid integer division and keep decimal precision.
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Scanner next() reads what?
A single token up to whitespace.
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Scanner nextLine() reads what?
The entire line including spaces.
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Common bug mixing nextInt() and nextLine()?
Leftover newline requires consuming nextLine first.
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What does FileNotFoundException indicate?
File path or name is incorrect or missing.
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Difference between relative and absolute path?
Relative is from project folder; absolute is full system path.
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What is a token?
Smallest meaningful unit read by Scanner (word, number).
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What happens if nextInt reads a non-int?
InputMismatchException.
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What does hasNextDouble check?
Whether next token is a valid double.
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What is loop tracing?
Simulating loops step-by-step to predict output.
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Purpose of nested loop tracing tables?
Helps determine variable values each iteration.
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What is time complexity of nested loops?
Usually O(n^2) when loops scale together.
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What is the loop invariant?
A condition that remains true throughout loop execution.
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What is the purpose of a loop counter?
Tracks iterations and controls loop progress.
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What happens if you modify loop variable inside the loop?
May cause unintended behavior or infinite loops.
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What is accumulation?
Adding values repeatedly inside a loop (e.g., sum += x).
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What is concatenation in loops?
Building strings by repeatedly adding substrings.
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Difference between ++i and i++?
++i increments then returns; i++ returns then increments.
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What is the scope of a variable declared in a loop header?
It exists only inside the loop.
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What is the purpose of using {} around loops?
Groups statements; without them only first line is inside loop.
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What does return do inside a loop?
Immediately exits the method.
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What is sentinel-controlled input?
Loop continues until a special sentinel value is entered.
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What is flag-controlled input?
Loop continues based on a boolean variable toggled when a condition occurs.
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Why should floating-point comparisons avoid == ?
Precision errors make exact comparison unreliable.
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What does System.out.print vs println do?
print stays on same line; println moves to next line.
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Why avoid hard-coded values?
Reduces flexibility and makes code harder to maintain.
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What happens if you open a Scanner on a file twice?
May cause errors or read pointer resets depending on implementation.
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Why close a Scanner reading a file?
Releases file resources.
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Does closing Scanner(System.in) close System.in?
Yes; can cause errors on further input.
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Why must hasNext be checked before next?
Calling next without a next token throws an exception.
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What does nextLine return if last input was nextInt?
An empty line due to leftover newline.
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What is string parsing?
Using methods to read specific characters/substrings.
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What does substring(begin,end) do?
Returns substring from begin up to end-1.
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What is charAt used for?
Accessing a single character at a specific index.
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What type does compareTo return?
An int:
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What is escape sequence \n?
Represents a newline.
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What is escape sequence \t?
Represents a tab.
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Why use equals instead of == for Strings?
#ERROR!
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What is the difference between compile-time and runtime errors?
Compile-time found before running; runtime occurs during execution.
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What is an algorithm?
Finite set of steps to solve a problem.
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What is pseudocode?
High-level description of an algorithm.
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What does trace table help with?
Tracking variable values across iterations.
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What is input sanitization?
Ensuring input meets expected format before processing.
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What is defensive programming?
Code written to handle unexpected inputs and errors.
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Why use constants (`final`)?
Improves clarity and prevents accidental changes.
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What is variable shadowing?
Local variable hides a variable declared outside.
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What does % operator compute?
Remainder of integer division.
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How do you check if a number is even?
num % 2 == 0
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How do you check if a number is odd?
num % 2 != 0
Note 
Flashcards (76)