exam review Flashcards

Question

How can you write a one-line conditional statement in Java?

Answer 1

You can write it without curly braces, e.g., if (x > y) y = x;. The if-statement ends at the first semicolon after the condition if no curly braces are present.

Answer 2

The conditional (ternary) operator is written as BoolExpression ? Value1 : Value2. If the boolean expression is true, it returns Value1; otherwise, Value2.

Answer 3

The order is: logical NOT (!), then multiplication/division/modulus (* / %), followed by addition/subtraction (+ -), relational, equivalence relational, logical AND, logical OR, and finally assignment (including combined assignments). Parentheses can alter the natural precedence.

Answer 4

A switch statement checks a test condition and has case labels: switch(testCondition) {
case condition:
// statements
break;
…
default:
// default statements
} Test conditions can be of type char, byte, short, int, or String.

Answer 5

Java 12 allows multiple case constants for a single case (e.g., case 1,3,5,7,9:) and an arrow syntax (case condition -> statement;) that can include multiple statements in a block. The new switch can also be used as an expression using yield to return a value.

Answer 6

- while loop: pretest loop executing 0 or more times (commonly used for input validation). - do-while loop: post-test loop executing at least once. - for loop: includes initialization, condition, and update sections; can be used with multiple variables and even with empty sections (for (;;) for an infinite loop). - Enhanced for loop: used for iterating over arrays or collections, e.g., for (dataType item : array) { ... }.

Answer 7

A sentinel value marks the end of input data, such as EOF or a specific value (e.g., -1) that signals termination of data input.

Answer 8

- continue skips the current iteration and moves to the next one. - break exits the loop entirely. (Note: Overuse can make code harder to read and debug.)

Answer 9

Arrays are objects that hold elements of a single type with a fixed size once created. They are declared as either int[] arr = new int[size]; or int arr[] = new int[size];. Arrays always have indices starting at 0, and they have a length field for size. Multi-dimensional arrays (jagged arrays and matrices) are also supported.

Answer 10

A vararg method accepts any number of arguments as an array. For example: public static int sum(int... numbers) can be called with different numbers of int arguments.

Answer 11

When the main method takes parameters (e.g., public static void main(String[] args)), command line arguments are passed as an array of strings. For example, running java CommandLineExample hello world passes "hello" and "world" as elements in args.

Answer 12

A method header includes the modifiers (e.g., public, static), the return type (e.g., void), the method name, and an argument list enclosed in parentheses.

Answer 13

The method signature consists of the method name and its parameter list. It is used by Java for binding—the process of matching a method call to the correct method definition (overloading based on parameter types, e.g., sum(int, int) vs. sum(double, double)).

Answer 14

Primitive types are passed by value (a copy is made) so changes do not affect the original. Object references are passed by value as well, but changes to the object’s data affect the original object (keeping in mind that strings are immutable).

Answer 15

Some classes provide default methods like toString(); these may be called implicitly or explicitly. They can be overridden using the @Override annotation.

Answer 16

A class is a blueprint for creating objects. It defines data (fields) and behavior (methods). In UML, a class diagram is divided into three sections: the class name, fields (with access specifiers), and methods (with signatures).

Answer 17

Instance members (fields/methods) belong to a specific object and are accessed via that object, while static members belong to the class itself and are shared across all instances.

Answer 18

A constructor is a special method called when a new object is created. It must have the same name as the class, has no return type, can be overloaded, and if none is provided, a default constructor is automatically created (setting numeric fields to 0, booleans to false, and object references to null).

Answer 19

Shadowing occurs when a local variable in a method has the same name as an instance field, thereby hiding the instance field. This can be resolved by using this.fieldName to refer to the instance field.

Answer 20

A shallow copy creates a new reference to the same object (both variables point to the same memory), while a deep copy creates an entirely new object with copies of the original object’s data, often done with a copy constructor.

Answer 21

Aggregation is a “has-a” relationship where one class contains references to objects of other classes (e.g., a course has an instructor and a textbook).

Answer 22

Returning direct references to private data can allow external modification, so it is safer to return a copy of the data to preserve encapsulation.

Answer 23

Java handles garbage collection automatically by reclaiming memory for objects that are no longer referenced (e.g., after setting an object reference to null).

Answer 24

An ArrayList is a resizable array provided by the Java Collections Framework. It automatically expands or shrinks, and offers methods like add, set, get, and remove. Its default capacity is 10 if not specified.

Answer 25

Exceptions are abnormal events during program execution. Checked exceptions (like file I/O issues) must be handled or declared, whereas unchecked exceptions (runtime exceptions and errors) do not require explicit handling, though they can occur (e.g., division by zero).

Answer 26

The call stack is a record of the active subroutines in a program. When an exception occurs, the stack trace lists the method calls leading to the exception, helping diagnose where the error happened.

Answer 27

A collection is a container that holds groups of objects. The main types include Lists (ordered sequence), Sets (unique elements), and Maps (key-value pairs).

Answer 28

- ArrayList: Fast random access via index; less efficient insertions/deletions in the middle. - LinkedList: Efficient insertions/deletions at the ends; slower random access. - Vector: Similar to ArrayList but with synchronized methods (thread-safe). - Stack: Inherits from Vector; follows LIFO (last in, first out) with methods such as push and pop.

Answer 29

A Queue is a FIFO (first in, first out) collection. Common methods include offer (add), poll (remove), remove, peek (examine first element), and element.

Answer 30

Maps store key-value pairs. A HashMap is optimized for efficient lookup, insertion, and deletion, while a TreeMap maintains the keys in sorted order, making traversal in order easier.

Answer 31

Linear search compares each element from index 0 to n. Its time complexity is O(n).

Answer 32

Binary search requires the array to be sorted in ascending order. It checks the middle element, then continues searching in either the left or right half. Its time complexity is O(log n).

Answer 33

Selection sort repeatedly selects the smallest value from the unsorted portion and moves it to the beginning, building a sorted portion of the array.

Answer 34

Big O notation describes the order of magnitude for algorithmic growth rates, focusing on worst-case scenarios. It ignores constant factors and non-dominant terms, allowing us to compare algorithm efficiency as input size increases.

Answer 35

The common hierarchy is: O(1) < O(log n) < O(n) < O(n log n) < O(n²) < O(n³) < O(2^n).

Answer 36

- O(log n): Binary search, GCD - O(n): Linear search - O(n log n): Merge sort - O(n²): Selection sort, insertion sort - O(2^n): Recursive solutions like Towers of Hanoi or certain Fibonacci implementations