Java Primitive Types and Casting

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Questions and Answers

How many total primitive types are there?

  • 7
  • 8 (correct)
  • 9
  • 6

Strings in Java are mutable.

False (B)

What is the purpose of the equals() method used with non-primitive types?

To compare actual values/content of the objects.

The method used to convert a string to an integer is __________.

<p>Integer.parseInt</p> Signup and view all the answers

Match the following Scanner methods with their functions:

<p>nextInt() = Reads an integer from the user input nextLine() = Reads an entire line of text from user input nextDouble() = Reads a double from the user input next() = Reads the next token from user input</p> Signup and view all the answers

Which of the following statements is true regarding widening casting?

<p>It is performed automatically. (D)</p> Signup and view all the answers

What does the charAt() method do?

<p>It extracts a single character from a string at a specified index.</p> Signup and view all the answers

The toLowerCase() method changes the letters of a string to uppercase.

<p>False (B)</p> Signup and view all the answers

What happens if a loop does not have an update that will eventually make the loop's condition false?

<p>The loop will run infinitely. (C)</p> Signup and view all the answers

Arrays in a programming language can store different data types simultaneously.

<p>False (B)</p> Signup and view all the answers

What is the correct declaration syntax for an array of integers?

<p>int [] arrayName</p> Signup and view all the answers

The first element in an array is accessed using the index _____ .

<p>0</p> Signup and view all the answers

Match the following array operations with their descriptions:

<p>Declaration = Specifying data type and size Instantiation = Creating the array and allocating memory Initialization = Assigning starting values to elements Traversing = Accessing elements in the array sequentially</p> Signup and view all the answers

Which of the following is the syntax for creating an array in Java?

<p>int[] numbers = new int[5]; (C)</p> Signup and view all the answers

The last index of an array with 5 elements is 5.

<p>False (B)</p> Signup and view all the answers

Describe what happens when you write to a file that already exists in the code example provided.

<p>The content of the file will be overwritten.</p> Signup and view all the answers

What is a method primarily used for?

<p>Bundling functionality (D)</p> Signup and view all the answers

A void method returns a value.

<p>False (B)</p> Signup and view all the answers

What is the term used when a method can be called multiple times throughout a program?

<p>Reusable</p> Signup and view all the answers

The method signature consists of the method's name and its __________.

<p>parameters</p> Signup and view all the answers

Match the following programming concepts with their definitions:

<p>Method Overloading = Same name, different parameters Static Method = Cannot access non-static methods Return Type = Indicates the type of data returned Loop Control Variable = Counter for iterations in a loop</p> Signup and view all the answers

Which operator is used to negate a boolean expression?

<p>! (C)</p> Signup and view all the answers

Short-circuited evaluation means the second operand of a logical expression is always evaluated.

<p>False (B)</p> Signup and view all the answers

What part of a for loop is executed only once before any evaluations?

<p>Initialization</p> Signup and view all the answers

The expression used to determine when a loop ends is known as the __________ statement.

<p>conditional</p> Signup and view all the answers

If a method is called without any parameters, what type of method is it?

<p>No-argument method (B)</p> Signup and view all the answers

Flashcards

Primitive Types

Data types that store actual values directly in memory.

Casting (Widening)

Automatically converting a smaller data type to a larger one.

Casting (Narrowing)

Manually converting a larger data type to a smaller one.

String Immutability

String values cannot be changed after they are created.

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String Initialization (Method 1)

Creating a String using "String variableName = "value";".

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String Initialization (Method 2)

Creating a String using "String variableName = new String("value");".

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Scanner Class

Java class that enables reading user input from the console.

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String substring()

Extracting part of a string. Returns a new string.

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For Loop (Standard)

Iterates over a block of code a specified number of times. Uses a counter variable to control the loop's execution.

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Enhanced For Loop

Iterates through each element in an array or collection, simplifying the loop's syntax and readability.

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Array Declaration

Declares an array variable specifying the data type and square brackets. Example: "int[] array1;"

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Array Instantiation

Allocates memory space for the array and specifies the number of elements. Example: "int[] numbers = new int[5];"

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Array Initialization (Quick Method)

Assigns initial values to the array elements directly during declaration. Example: "int[] numbers = {1, 2, 3, 4, 5};"

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Array Length

Represents the number of elements in an array. Example: "int length = myArray.length;"

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Array Element Access

Retrieving or modifying the value of a specific element at a particular index. Example: "myArray[2] = 3;"

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Array Traversal

Iterating through each element in an array sequentially using a loop.

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Method: What is it?

A reusable block of code that performs a specific task, like adding two numbers or printing something to the screen. They make your code more organized and efficient.

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Method Components

Methods have several parts: the return type (data type of the output), the name, and the parameters (input values).

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Method Declaration

Writing the method's code structure, including the return type, name, and parameters. This sets up the method for use.

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Method Signature

The method's name and the list of parameter types. It uniquely identifies a method.

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Method Overloading

Having multiple methods with the same name but different parameter lists within the same class. The compiler chooses the appropriate method based on the arguments.

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Calling a Method

Executing a method's code, providing the necessary arguments if required.

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Conditional Statements

Instructions in your code that execute different parts of the code based on whether a condition is true or false.

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One-Way Selection

A conditional statement that executes a block of code only when a specific condition is true.

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Logical Operators

Operators (!, &&, ||) that combine Boolean values to create complex conditions.

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For Loop: The Goal

A loop structure that executes a block of code repeatedly for a specific number of times.

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Study Notes

Primitive Types

  • Primitive types are data types that store actual values directly in memory.
  • There are 8 fundamental primitive types.
  • Examples include int, double, boolean, and char.

Casting

  • Widening Casting (automatic): Automatically converts a smaller data type to a larger one. This is automatic, no explicit action required.
  • Example: byte to short, short to int, int to double.
  • Narrowing Casting (manual): Manually converts a larger data type to a smaller one. Requires explicit type casting.
  • Example: double to int, float to long.

Strings

  • Strings are non-primitive data types.
  • They store a pointer to the actual string value in memory.
  • Strings are immutable; their value cannot be changed after creation.

Initialization

  • Strings can be initialized in two ways:
  • String myString = "hello"; (string literal)
  • String myString = new String ("hello"); (using the String class)

Substring

  • Extracts a portion of a string.
  • substring(startIndex, endIndex) returns a new string containing characters from startIndex (inclusive) up to, but not including, endIndex.

charAt() Method

  • Used to access a single character from a string at a specified index.
  • Example: char firstChar = myString.charAt(0);

toLowerCase()/toUpperCase() Methods

  • toLowerCase() converts the entire string to lowercase.
  • toUpperCase() converts the entire string to uppercase.

contains() Method

  • Checks if a string contains another string as a substring. Returns a boolean.

String to Integer Conversion

  • Converts a string representation of an integer to an integer value.
  • Example: int myInt = Integer.parseInt(myString);

Integer to String Conversion

  • Converts an integer value to its string representation.
  • Example: String myString = "" + myInt; or String myString = Integer.toString(myInt)

Scanner Class

  • Used to obtain input from the user.
  • Initialized with Scanner scanner = new Scanner(System.in); to read input from the console.
  • Methods like nextInt(), nextDouble(), nextLine(), etc are used to read different input types from the user.

Methods

  • Methods bundle functionality into reusable units.
  • They have a name, parameters (input data), and a return type (output data).
  • Method signatures include method name and parameters to differentiate between methods.

Boolean expressions and If Statements

  • Boolean expressions evaluate to true or false.
  • if statements control the flow of execution based on the result of boolean expressions.

Loops: For Loops

  • For loops iterate a specific number of times.
  • They have an initialization, a condition, and an increment/decrement statement.

Loops: While Loops

  • While loops repeatedly execute a block of code as long as a specified condition evaluates to true.

Arrays

  • Arrays store collections of related data.
  • Each element in an array is accessed by its index (starting from 0).

Files

  • Methods to write and read data to/from files.
  • File handling involves creating an input/output stream object to interact with the file.

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