Java Programming Basics Flashcards

Question 1

What is a variable in Java, and why do programs use them?

Accepted Answer

A variable is a named storage location in memory that holds a value of a specific type. Programs use variables to store data, read it later, and change it as the program runs. In Java, you declare a variable by writing its type followed by its name, and may assign an initial value.

Question 2

What are the eight primitive data types in Java?

Accepted Answer

Java has eight primitive types: byte, short, int, and long for whole numbers, float and double for decimal numbers, char for a single Unicode character, and boolean for true or false values. Primitives hold their values directly rather than referring to objects. The int type is the usual default choice for whole numbers.

Question 3

What is the difference between the assignment operator and the equality operator?

Accepted Answer

The single equals sign assigns a value to a variable, while the double equals sign compares two values and produces a boolean result. For example, x = 5 stores five in x, but x == 5 asks whether x currently holds five. Confusing the two is a common beginner mistake.

Question 4

What does integer division produce when both operands are int values?

Accepted Answer

Integer division produces an integer result, so any fractional part is discarded rather than rounded. For example, 7 divided by 2 yields 3, not 3.5. To get a decimal result, at least one operand must be a floating point type, such as double, as in 7.0 / 2.

Question 5

How does the increment operator differ when placed before versus after a variable?

Accepted Answer

A prefix increment, ++x, adds one first and then uses the new value. A postfix increment, x++, uses the current value first and adds one afterward. For example, when x is 5, the statement y = ++x sets y to 6, while y = x++ sets y to 5.

Question 6

What is the purpose of the final keyword applied to a variable?

Accepted Answer

The final keyword makes a variable a constant, so it can be assigned exactly once and cannot be changed afterward. Programmers often use final for values that should never change, such as a maximum size or a fixed rate. Reassigning a final variable causes a compile time error, which helps catch mistakes early.

Question 7

How does Java handle the order of operations in arithmetic expressions?

Accepted Answer

Java follows standard mathematical precedence, so multiplication, division, and remainder are evaluated before addition and subtraction. Operators with equal precedence are generally evaluated from left to right. Parentheses override these rules, so writing (2 + 3) * 4 produces 20 while 2 + 3 * 4 produces 14.

Question 8

Why does Java use the boolean type for conditions in if statements?

Accepted Answer

An if statement needs an expression that evaluates to true or false, and the boolean type represents exactly those two values. Java does not treat numbers as truth values, so if (count) with an int fails to compile. Instead, write a comparison such as if (count > 0) to produce a boolean.

Question 9

What is the difference between a while loop and a do while loop?

Accepted Answer

A while loop checks its condition before each pass, so the body may run zero times if the condition starts out false. A do while loop runs its body first and then checks the condition, so the body always runs at least once. Use do while when the body must run at least once.

Question 10

How does a for loop combine initialization, condition, and update in one line?

Accepted Answer

A for loop places three parts inside its parentheses, separated by semicolons: an initialization that runs once, a condition checked before each iteration, and an update that runs after each iteration. For example, for (int i = 0; i < 5; i++) counts from zero through four.

Question 11

What is the purpose of the break statement inside a loop?

Accepted Answer

The break statement immediately exits the innermost loop or switch statement that contains it. Execution then continues with the first statement after that block. Break is useful when a search finds its target early and remaining iterations would be wasted work.

Question 12

How does a switch statement differ from a chain of if else statements?

Accepted Answer

A switch statement compares one value against several constant case labels, which often makes code easier to read than many if else tests. Each case typically ends with break, otherwise execution falls through into the next case. Arrow style case labels, available in newer Java versions, avoid fall through entirely.

Question 13

What does the continue statement do inside a loop body?

Accepted Answer

The continue statement skips the rest of the current iteration and moves directly to the next iteration. In a for loop, the update expression still runs before the condition is checked again. Continue is helpful for ignoring certain values without nesting the main logic inside another if block.

Question 14

How do nested loops behave when an inner loop runs inside an outer loop?

Accepted Answer

For each single iteration of the outer loop, the inner loop runs to completion. If the outer loop runs three times and the inner loop runs four times, the body executes twelve times in total. Nested loops are common for working with grids and tables, but deep nesting can make programs slow.

Question 15

What is an enhanced for loop, and what kind of collections can it traverse?

Accepted Answer

The enhanced for loop, also called the for each loop, iterates over every element of an array or any object implementing Iterable. Its syntax is for (String name : names), which reads as for each name in names. It is simpler than an index based loop when you only need to read each element.

Question 16

Why might an infinite loop occur, and how can a programmer prevent one?

Accepted Answer

An infinite loop occurs when the condition never becomes false, usually because the loop variable is not updated or the update moves in the wrong direction. Programmers prevent this by checking that the condition eventually fails and that each iteration moves closer to that outcome. A debugger or printed output can reveal the problem.

Question 17

What is a method in Java, and what problem does it solve?

Accepted Answer

A method is a named block of code that performs a specific task and can be called from other places in the program. Methods solve the problem of repeating the same instructions, because you write them once and reuse them with different inputs. They also make programs easier to read, test, and maintain.

Question 18

What do the parameters and return type tell you about a method's signature?

Accepted Answer

The parameter list names the inputs a method expects, along with each input's type, and the return type states what kind of value the method sends back. A void return type means the method performs an action without returning a value. Together, these details define how callers must use the method.

Question 19

How does Java pass arguments to methods, by value or by reference?

Accepted Answer

Java always passes arguments by value, meaning the method receives a copy. For primitives, changes inside the method do not affect the caller's variable. For objects, the copy is of the reference, so the method can change the object's contents but cannot make the caller's variable point somewhere else.

Question 20

How do you declare and create an array of five integers in Java?

Accepted Answer

You can write int[] numbers = new int[5]; which declares a reference named numbers and allocates space for five int values. Each element starts with the default value zero. Alternatively, int[] numbers = {4, 8, 15, 16, 23}; creates and fills the array in one step.

Question 21

What happens when a program accesses an array index that is out of bounds?

Accepted Answer

Java throws an ArrayIndexOutOfBoundsException at runtime, which stops the program unless the exception is caught. Valid indexes run from zero through the array length minus one. Checking the index against array.length before access is a simple way to avoid this error.

Question 22

How can you find the length of an array versus the length of a String?

Accepted Answer

For an array, you read the length field without parentheses, as in numbers.length. For a String, you call the method with parentheses, as in name.length(). Keeping these two forms straight prevents a common group of compile errors for beginners learning the language.

Question 23

What is method overloading, and how does Java choose which version to call?

Accepted Answer

Method overloading means defining several methods with the same name but different parameter lists. Java chooses the version by matching the number and types of the arguments at compile time. Return type alone cannot distinguish overloads, so a method differing only by return type is not allowed.

Question 24

What does a recursive method need in order to avoid running forever?

Accepted Answer

A recursive method needs a base case, which is a condition where it returns a result without calling itself again. Each recursive call must also move the problem closer to that base case. Without both, the calls never stop and the program eventually fails with a stack overflow error.

Question 25

What is the difference between a class and an object?

Accepted Answer

A class is a blueprint that describes the fields and methods a kind of thing will have, while an object is a specific instance created from that blueprint. You can create many objects from a single class, each with its own values.

Question 26

What is the purpose of a constructor in a Java class?

Accepted Answer

A constructor is a special method that runs when an object is created, and it initializes the object's fields. It has the same name as the class and no return type. If you do not write any constructor, Java supplies a default one that takes no arguments.

Question 27

What are access modifiers, and why do they matter?

Accepted Answer

Access modifiers such as private, protected, and public control which other code can read or call a class member. Marking fields private and exposing them through methods is a common way to protect an object's data. Choosing the narrowest access that still works keeps code easier to change safely.

Question 28

What is encapsulation, and how do getters and setters support it?

Accepted Answer

Encapsulation means bundling data and the methods that operate on it inside one class, while hiding internal details from outside code. Getters read a private field, and setters change it, often with validation in between. This lets the class enforce rules, such as rejecting a negative age, without callers knowing how data is stored.

Question 29

What does the this keyword refer to inside an instance method?

Accepted Answer

The this keyword refers to the current object, the one whose method is running. It is commonly used to distinguish a field from a parameter with the same name, as in this.name = name. It can also pass the current object to another method or call another constructor.

Question 30

What is inheritance, and what keyword does Java use to express it?

Accepted Answer

Inheritance lets one class, called a subclass, acquire the fields and methods of another class, called its superclass. Java expresses this relationship with the extends keyword, as in class Dog extends Animal. Subclasses can reuse shared behavior and add or override methods to specialize it.

Question 31

How does overriding a method in a subclass differ from overloading one?

Accepted Answer

Overriding happens when a subclass provides its own version of an inherited method with the same name and parameter list, and Java chooses the version based on the actual object type at runtime. Overloading happens within one class when the parameter lists differ, and the choice is made at compile time.

Question 32

What is the purpose of the static keyword on a field or method?

Accepted Answer

A static member belongs to the class itself rather than to any particular object, so it is shared by all instances. Static methods can be called using the class name, as in Math.max, without creating an object first. Static methods cannot directly access instance fields because no particular object exists when they run.

Question 33

What is an exception in Java, and how does it differ from a compile error?

Accepted Answer

An exception is an event that disrupts normal program flow, usually signaled by an object describing the problem. A compile error is detected before the program runs, when the compiler finds code it cannot translate. Exceptions typically occur during execution, when conditions such as a missing file or bad input appear unexpectedly.

Question 34

How does a try catch block handle an exception that might occur?

Accepted Answer

The code that might fail goes inside the try block, and a matching catch block contains the recovery steps. If an exception of the named type occurs, Java skips the rest of the try block and runs the catch block instead. If no exception occurs, the catch block is skipped entirely.

Question 35

What is the difference between checked and unchecked exceptions?

Accepted Answer

Checked exceptions, such as IOException, must be either caught or declared in the method signature with throws, and the compiler enforces this rule. Unchecked exceptions, which extend RuntimeException, do not require this handling, and they often signal programming mistakes such as dividing by zero. Both types can be caught when that is appropriate.

Question 36

What is the purpose of the finally block in exception handling?

Accepted Answer

A finally block contains code that runs whether or not an exception occurred, making it useful for cleanup. Typical uses include closing files, releasing locks, or closing network connections. The block runs even when the try or catch block contains a return statement.

Question 37

How can a program read text typed by a user from the console?

Accepted Answer

A common approach uses the Scanner class from java.util, created with new Scanner(System.in). Calling nextLine() reads an entire line of text as a String, while nextInt() reads the next integer. Remember to import java.util.Scanner at the top of the file before using it.

Question 38

Why should a program close a Scanner after it finishes reading input?

Accepted Answer

Closing a Scanner releases the underlying resources, such as the file or stream it reads from, so the operating system is not left holding them. Using try with resources is a clean way to close the scanner automatically once its block ends.

Question 39

How does Java handle integer parsing errors when converting user text to a number?

Accepted Answer

Methods such as Integer.parseInt convert a String to an int, but they throw a NumberFormatException when the text is not a valid whole number. Programs usually wrap the call in a try block and catch that exception. The catch block can then ask the user to try again instead of crashing.

Question 40

What is the purpose of the main method, and what signature does Java require?

Accepted Answer

The main method is the entry point where the Java runtime begins executing a standalone program. The standard signature is public static void main(String[] args), and the args parameter receives any command line arguments as an array of strings. Without a correctly declared main method, the program cannot start.

Java Programming Basics Flashcards

1Variables, Data Types, and Operators

2Control Flow Statements

3Methods and Arrays

4Classes and Objects

5Exceptions and Program Input

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