Essential Java Cheatsheet Table 101: Quick Java Reference

== checks if two object references point to the same memory location.
.equals() checks if two objects are logically equivalent, often comparing their values.

The four key principles are:
Encapsulation: Hiding data using private fields and providing access through methods.
Inheritance: Reusing code by deriving classes from parent classes.
Polymorphism: Allowing methods to behave differently based on context (overloading and overriding).
Abstraction: Defining abstract classes or interfaces for implementation details.

Final variable: Its value cannot be changed once assigned.
Final method: Cannot be overridden by subclasses.
Final class: Cannot be subclassed.

The Java Collections Framework provides data structures like List, Set, and Map.
List: Ordered collection (e.g., ArrayList, LinkedList).
Set: No duplicate elements (e.g., HashSet, TreeSet).
Map: Key-value pairs (e.g., HashMap, TreeMap).

Garbage collection is an automatic memory management feature in Java. It removes objects that are no longer referenced, freeing up memory for other processes. You can suggest garbage collection with System.gc(), but it is managed by the JVM.

String: Immutable sequence of characters.
StringBuilder: Mutable, fast, not thread-safe.
StringBuffer: Mutable, slower, thread-safe.

Multithreading allows concurrent execution of two or more threads to perform tasks simultaneously.
Use Thread class or implement Runnable interface.
Methods: start(), run(), sleep(), join().

The try-with-resources statement ensures that resources like files or sockets are closed automatically after use.
Example:
try (
BufferedReader br = new BufferedReader(new FileReader("file.txt"))) {
System.out.println(br.readLine());
}

Checked exceptions: Must be handled during compilation (e.g., IOException, SQLException).
Unchecked exceptions: Occur during runtime and don’t need explicit handling (e.g., NullPointerException, ArithmeticException).

Static variable: Shared among all instances of a class.
Static method: Called without creating an instance of the class.
Static block: Executes once when the class is loaded.
Example:
class Example {
static int count = 0;
static void showCount() {
System.out.println(count);
}
}