Lecture2b-variables-Identifiers-data-types-assignments Flashcards
What is an identifier in Java?
A name used for variables, classes, or methods.
What are reserved words in Java?
Special words (e.g., int, double, class) that cannot be used as variable names.
What are the three main parts of a variable?
- Name (Identifier)
-
Data Type (e.g.,
int,double) - Value (Stored data)
Example: int count = 1;
What is the difference between local and global variables?
✔ Local Variable: Exists only inside the method where it’s declared.
✔ Global Variable: Exists throughout the entire program.
What are Java’s 8 primitive data types?
- byte
- short
- int
- long
- float
- double
- char
- boolean
What are Java’s integer data types?
✔ byte: -128 to 127
✔ short: -32,768 to 32,767
✔ int: -2,147,483,648 to 2,147,483,647
✔ long: Very large numbers
What are Java’s floating-point data types?
✔ float – Stores decimal numbers with 7 digits of precision.
✔ double – Stores decimal numbers with 15 digits of precision.
What values can a boolean hold?
true or false
Example:
```java
boolean isJavaFun = true;
~~~
How do you declare a char in Java?
java char letter = 'A';
✔ Uses single quotes (‘ ‘)
✔ Stores one character
How do you declare a String in Java?
java String name = "Java";
✔ Strings use double quotes (“ “)
✔ Strings are objects, not primitive types.
What does the + operator do with strings?
Joins (concatenates) strings.
Example:
java
System.out.println("Hello " + "World!");
🔹 Output:
Hello World!
How do you declare a constant?
Use final to prevent changes.
java final int MAX_SPEED = 120;
✔ Constants use ALL UPPERCASE
What is an assignment statement in Java?
Stores a value in a variable using =.
Example:
java int x = 5;
🔹
x is assigned the value 5.How does Java handle division and remainder operations?
✔ Integer division (/) drops decimals (e.g., 7 / 2 = 3)
✔ Modulus (%) gives the remainder (e.g., 7 % 2 = 1)
How do you calculate exponents in Java?
Use Math.pow(base, exponent).
Example:
```java
System.out.println(Math.pow(2, 3)); // Output: 8.0
~~~
What are ++ and -- used for?
✔ x++ → Adds 1 (x = x + 1)
✔ x-- → Subtracts 1 (x = x - 1)
What are Java’s compound operators?
✔ += (Addition assignment)
✔ -= (Subtraction assignment)
✔ *= (Multiplication assignment)
✔ /= (Division assignment)
✔ %= (Modulus assignment)
Example:
```java
x += 5; // Equivalent to x = x + 5;
~~~
What are the two types of data conversion?
-
Widening Conversion (Safe) – Converts small to large (e.g.,
int → double). -
Narrowing Conversion (Unsafe) – Converts large to small (e.g.,
double → int).
Example of casting:
```java
double num = 10.5;
int x = (int) num; // x = 10
~~~
What are the three types of data conversion in Java?
-
Assignment Conversion: Assigning a smaller type to a larger one automatically (e.g.,
int → double). -
Promotion: Automatic conversion in expressions (e.g.,
int + double = double). -
Casting: Manually converting types using
(type)(e.g.,(int) 3.5→3).
What is JShell in Java?
A Read-Evaluate-Print Loop (REPL) that allows testing Java code interactively.
Example usage:
```sh
jshell> int x = 5;
x ==> 5
jshell> x + 3;
$2 ==> 8
jshell> /exit
~~~
What is casting in Java, and how is it used?
Casting is manually converting one data type into another using (type).
What is Widening Cast in Java?
Widening Cast is a safe, automatic conversion from a small to a large type.
Example:
```java
int num = 10;
double d = num; // Implicit casting (int to double)
~~~
What is Narrowing Cast in Java?
Narrowing Cast is an explicit, risky conversion from a large to a small type.
Example:
```java
double d = 10.99;
int num = (int) d; // Explicit casting (double to int), drops decimals
~~~
When is casting used in Java?
Casting is used when Java does not automatically convert types.
What are numeric literals in Java?
A numeric literal is a constant value written directly in code.
What is an integer literal?
An integer literal is a whole number written directly in code.
Example: int years = 34; // 34 is an integer literal
What is a floating-point literal?
A floating-point literal is a number that has a decimal point written directly in code.
Example: double pi = 3.14159; // 3.14159 is a floating-point literal
What is a caution regarding integer literals?
Integer literals must fit within the variable’s type (byte, short, int, long).
