likhitha manikonda

Posted on Oct 21 • Edited on Oct 27

Java vs Python for Beginners: A Syntax Perspective

#java #beginners #python #programming

🐍 Python vs ☕ Java — Ordered Beginner’s Guide with Keywords, and Examples

A single, ordered reference that covers core concepts, short plain-language explanations, highlighted keywords, and tiny code examples you can read at a glance.

1. 💬 Comments

Used to leave notes in code that the computer ignores.

Keywords: # (Python), // (Java)

Python

# this is a comment

Java

// this is a comment

2. 🔠 Indentation and Code Blocks

Indentation groups code in Python; curly braces {} do it in Java. Wrong indentation in Python changes behavior.

Keywords: indentation, { }
Python

def greet():
    print("Hello")  # indented block

Java

void greet() {
    System.out.println("Hello"); // block inside { }
}

3. 🧾 Input Output and Taking Multiple Inputs

Get input from user and show output. Use .split() in Python for many values on one line; Java’s Scanner reads values one by one.

Keywords: input(), print(), Scanner, nextInt()

Python

x, y = input("Enter two values: ").split()
print(x, y)

Java

Scanner sc = new Scanner(System.in);
int x = sc.nextInt();
int y = sc.nextInt();
System.out.println(x + " " + y);

4. 🔁 Type Casting Conversions

Change data type (text → number, or double → int).

Keywords: int(), float(), Integer.parseInt(), Double.parseDouble(), (int)

Python

x = int("5")      # "5" -> 5
d = float("3.14")

Java

int x = Integer.parseInt("5");
double d = Double.parseDouble("3.14");
int n = (int) 3.9; // cast

5. 📦 Variable Types and Basic Data Types

Where you store values. Python is dynamically typed; Java is statically typed.

Keywords: int, float, double, bool, boolean, str, String

Python

a = 5         # int
b = 3.14      # float
c = True      # bool
s = "hi"      # str

Java

int a = 5;
double b = 3.14;
boolean c = true;
String s = "hi";

6. ➕ Operators and Conditionals with Comparison Ops

Math and comparisons. Comparison operators: ==, !=, >, <, >=, <=. Logical: Python and/or/not, Java && / || / !.

Keywords: ==, !=, >, <, >=, <=, and, or, not, &&, ||, !

Python

if x == 5 and y != 0:
    print("ok")

Java

if (x == 5 && y != 0) { System.out.println("ok"); }

7. 🗝️ Keywords Common Reserved Words

Short list to recognize everywhere.

Python examples: def, class, if, else, elif, import, return, pass, lambda, True, False, None.

Java examples: public, private, protected, static, void, class, if, else, return, new, final, abstract, extends, implements.

8. 🔍 Conditionals If Elif Else

Make decisions based on comparisons and logical operators.

Keywords: if, elif (Python), else if (Java), else

Python

if x > 0:
    print("positive")
elif x == 0:
    print("zero")
else:
    print("negative")

Java

if (x > 0) {
  System.out.println("positive");
} else if (x == 0) {
  System.out.println("zero");
} else {
  System.out.println("negative");
}

9. 🔂 Loops For While Nested Loops

Repeat actions. Use for for fixed iteration, while for condition loops. Nested loops are loops inside loops for grids or pairs.

Keywords: for, while, range, break, continue
Python

for i in range(3): print(i)
while x < 3: x += 1

# nested loop
for i in range(2):
    for j in range(2):
        print(i, j)

Java

for (int i=0;i<3;i++) System.out.println(i);
while (x<3) x++;

for (int i=0;i<2;i++) {
  for (int j=0;j<2;j++) {
    System.out.println(i + " " + j);
  }
}

10. 🕳️ Pass Statement

Placeholder when code is syntactically required but you don’t want it to run yet.

Keywords: pass

def todo():
    pass

(Java: use empty {} or comment)

11. 📦 Modules Packages Code Organization

Group code into files and folders for reuse.

Keywords: module, package, import, init.py

Python

# greet.py
def say_hi(): print("Hi")
import greet
greet.say_hi()

Java

package mypkg;
public class Greet { public static void sayHi(){ System.out.println("Hi"); } }
// use import mypkg.Greet;

12. 🧮 Functions Methods Arguments Multiple Arguments

Functions perform tasks; methods belong to classes. Python supports *args and **kwargs; Java supports varargs ....

Keywords: def, return, *args, **kwargs, void

Python

def greet(name): return "Hello " + name
def all_args(*args, **kwargs): print(args, kwargs)

Java

void greet(String name) { System.out.println("Hello " + name); }
void many(String... vals) { System.out.println(Arrays.toString(vals)); }

13. 🔁 Recursion Recursive Functions

A function calls itself to handle smaller parts of a problem; must have a base case.

Keywords: recursion, base case, return

Python

def fact(n):
    return 1 if n == 0 else n * fact(n-1)

Java

int fact(int n) { return (n==0) ? 1 : n * fact(n-1); }

14. ⚡ Lambda Functions

Tiny anonymous functions for quick one-line operations.

Keywords: lambda, ->

Python

square = lambda x: x*x
print(square(3))  # 9

Java

Function<Integer,Integer> square = x -> x * x;

15. 🧭 map filter and Streams

Apply function to all items (map) or select items that pass a test (filter). Java Streams are similar.

Keywords: map, filter, stream, collect

Python

nums = [1,2,3]
print(list(map(lambda x:x*2, nums)))
print(list(filter(lambda x:x%2==0, nums)))

Java

List<Integer> doubled = nums.stream().map(x->x*2).collect(Collectors.toList());

16. 🧺 Data Structures

— Ways to store and organize collections of values

Concept	Python (easy)	Java (similar)
List	`list: [1,2,3]`	`ArrayList`
Tuple	`tuple: (1,2,3)`	`LinkedList` (similar)
Dictionary	`dict: {'a':1}`	`HashMap`
Set	`set: {1,2,3}`	`HashSet`
Array	`array` module	`int[]`, `String[]`

Examples:

Python

my_list = [1,2]
my_dict = {"a":1}
my_set = {1,2}
my_tuple = (1,2,3)
import array
arr = array.array('i', [1,2,3])

Java

List<Integer> list = Arrays.asList(1,2);
Map<String,Integer> map = new HashMap<>();
Set<Integer> set = new HashSet<>();
List<Integer> linked = new LinkedList<>(Arrays.asList(1,2,3));
int[] arr = new int[3];
String[] names = new String[] {"a","b"};

Keywords: list, tuple, dict, set, ArrayList, LinkedList, HashMap, HashSet, int[], String[].

17. 🐾 Classes, Objects, Constructor, Inheritance

🐾 Classes

Definition: A blueprint that describes the properties (data) and behaviors (methods) that objects created from the class will have.

Keywords: class, public/private/def (Python), class (Java)

Python (simple class):

class Animal:
    species = "Unknown"   # class variable

    def __init__(self, name):
        self.name = name  # instance variable

    def speak(self):
        print(self.name + " makes a sound")

Java (simple class):

public class Animal {
    public static String species = "Unknown"; // class variable
    String name; // instance variable

    public void speak() {
        System.out.println(name + " makes a sound");
    }
}

Notes:

Classes group related data and functions.
Class variables are shared by all instances; instance variables are per object.

🧱 Objects

Definition: A concrete instance created from a class. Objects hold their own data according to the class blueprint.

Keywords: instance, new (Java), object creation

Python (create object):

a = Animal("Buddy")
a.speak()  # Buddy makes a sound

Java (create object):

Animal a = new Animal();
a.name = "Buddy";
a.speak(); // Buddy makes a sound

Notes:

Multiple objects can be created from the same class; each has independent instance variables.
Methods are called on objects to perform actions or access data.

🔧 Constructor

Definition: A special method that runs when an object is created; used to initialize instance variables.

Keywords: init (Python), constructor (Java, same name as class), new (Java object creation)

Python constructor:

class Animal:
    def __init__(self, name, age=0):  # __init__ is the constructor
        self.name = name
        self.age = age

Java constructor:

public class Animal {
    String name;
    int age;
    public Animal(String name, int age) { // constructor
        this.name = name;
        this.age = age;
    }
}

Notes:

Constructors can be overloaded in Java (multiple constructors with different parameters).
Python supports default parameter values instead of overloading.

🌱 Inheritance

Definition: A mechanism where a new class (child/subclass) derives properties and behaviors from an existing class (parent/superclass). This promotes code reuse and polymorphism.

Keywords: extends (Java), class Child(Parent): (Python), super(), @override (Java)

Python inheritance:

class Animal:
    def speak(self):
        print("Animal sound")

class Dog(Animal):            # Dog inherits from Animal
    def speak(self):
        super().speak()       # call parent method
        print("Dog barks")

Java inheritance:

class Animal {
    void speak() { System.out.println("Animal sound"); }
}
class Dog extends Animal {
    @Override
    void speak() {
        super.speak();         // call parent method
        System.out.println("Dog barks");
    }
}

Notes:

Child classes get parent methods and fields by default.
Use super() (Python/Java) to call the parent class constructor or methods.
Java supports single inheritance for classes (interfaces allow multiple contracts); Python supports multiple inheritance.

18. 🔐 Encapsulation ✅ Access Modifiers

— Who can see or change class data

Concept	Python (convention)	Java (keyword & meaning)
Public	No underscore; accessible everywhere	public — accessible from any class
Protected	`_name` — single underscore (convention only)	protected — accessible within package and subclasses
Private	`__name` — double underscore (name mangling)	private — accessible only inside the class
Package / Module	Module-level (no explicit keyword) — module encapsulation	(default, no keyword) — package-private when no modifier used
Final / Read-only	Use convention or property; no keyword to forbid reassignment	final — prevents reassignment (variable) or extension (class)

Examples

Python

class Person:
    name = "public"      # public by convention
    _secret = "protected" # protected by convention
    __private = "private" # name-mangled (class-private)

    @property
    def private(self):
        return self.__private

Java

public class Person {
    public String name;         // public
    protected String secret;    // protected
    private String privateData; // private
    String pkgData;            // package-private (no modifier)
    public final int ID = 1;    // final (read-only)
}

Keywords: public, protected, private, final, (no modifier → package-private in Java; single _ and double __ are Python naming conventions).

19. 🧷 Static Methods and Class vs Instance Variables Examples

Static/class-level belongs to the class; instance-level belongs to each object.

Keywords: static, @staticmethod, class variable, instance variable

Python:

class Counter:
    count = 0
    def __init__(self): Counter.count += 1
    @staticmethod
    def info(): print("Counter class")
c1 = Counter(); c2 = Counter()
print(Counter.count)  # 2
Counter.info()

Java:

class Counter {
    static int count = 0;
    Counter() { count++; }
    static void info(){ System.out.println("Counter class"); }
}
new Counter(); new Counter();
System.out.println(Counter.count); // 2
Counter.info();

20. 🧱 Abstraction Abstract Classes Methods

Expose only what’s necessary and hide implementation. Python uses ABC, Java uses abstract.

Keywords: abstract, ABC, @abstractmethod

Python

from abc import ABC, abstractmethod
class Animal(ABC):
    @abstractmethod
    def make_sound(self): pass

Java

abstract class Animal { abstract void makeSound(); }

Abstract classes — simple explanation

Python: use the abc module and make a class inherit ABC, mark required methods with @abstractmethod; subclasses must implement those methods or you get an error at runtime.
Java: use the abstract keyword on a class or method; the compiler forces subclasses to implement abstract methods or be declared abstract themselves.
Main practical difference: Python’s check happens at runtime and lets you mix multiple abstract bases; Java’s check happens at compile time and a class can extend only one other class (use interfaces for multiple contracts).

21. 🧩 Interfaces vs Protocols Examples

Define a required set of methods (contract). Java uses interface; Python can use Protocol or duck typing.

Keywords: interface, implements, Protocol, duck typing

Java:

interface Animal { void makeSound(); }
class Dog implements Animal { public void makeSound(){ System.out.println("Bark"); } }

Python:

from typing import Protocol
class Animal(Protocol):
    def make_sound(self) -> None: ...
class Dog:
    def make_sound(self) -> None: print("Bark")

None vs Ellipsis vs Return Nothing

Concept	Python (meaning + short snippet)	Java (meaning + short snippet)	Keywords
None vs null	No value. Example: `x = None; def f(): pass; print(f())`	No reference. Example: `String s = null; System.out.println(s);`	None, null
Ellipsis `...`	Placeholder/stub. Example: `def todo(): ...`	No `Ellipsis` object; use empty body, exception, or abstract method: `void todo() { }` or `abstract void call();`	..., Ellipsis, abstract
`-> None` vs `void`	Type hint: function returns nothing. Example: `def greet() -> None: print("Hi")`	Method returns nothing. Example: `void greet() { System.out.println("Hi"); }`	-> None, void

None / null

Python — No value; functions without return return None

x = None
def f():
    pass
print(x)   # None
print(f()) # None

Java — No reference to an object; similar concept is null

String s = null;
void doNothing() { }
System.out.println(s); // prints "null"

Ellipsis `...` (placeholder)

Python — Lightweight placeholder used in stubs or Protocols

def todo(): ...
class API:
    def call(self) -> None: ...

Java — No Ellipsis object; common placeholder patterns

void todo() { }                                 // empty method body
void notSupported() { throw new UnsupportedOperationException(); }
abstract class API { abstract void call(); }     // contract without implementation

`-> None` (Python) vs `void` (Java)

Python — Type hint that the function returns nothing

def greet() -> None:
    print("Hi")

def api_stub() -> None: ...

Java — Method signature that returns nothing

void greet() {
    System.out.println("Hi");
}

abstract void apiStub(); // declaration with no implementation

Keywords recap: None, null, ..., Ellipsis, -> None, void, abstract.

22. 🦴 Polymorphism Overriding Overloading and super

Overloading: Same method name, different behavior. Use super() to call parent method. Java supports overloading; Python uses defaults or args.

Keywords: **override, **overload, *@override*, **super()*

Python Overriding:

class Parent:
    def say(self): print("P")
class Child(Parent):
    def say(self):
        super().say()
        print("C")
Child().say()

Java Overriding:

class Parent { void say(){ System.out.println("P"); } }
class Child extends Parent {
  @Override void say(){ super.say(); System.out.println("C"); }
}
new Child().say();

Java overloading:

class Greet {
  void greet() { System.out.println("Hi"); }
  void greet(String name) { System.out.println("Hi " + name); }
}

23. 🔗 Pass by Value vs Reference

How arguments are passed to functions/methods. Mutability matters.

Keywords: mutable, immutable, primitive, reference

Python:

def change(l): l.append(4)
l=[1,2,3]; change(l); print(l)  # [1,2,3,4]

Java:

void change(int x){ x = 10; } // caller unchanged
void add(List<Integer> l){ l.add(4); } // object modified

24. 📁 File Handling Read Write

Open, read, write files. Use with in Python to auto-close files. Java offers NIO Files.

Keywords: open, with, read, write, Files

Python:

with open("file.txt","w") as f:
    f.write("Hello")
with open("file.txt","r") as f:
    print(f.read())

Java:

Files.writeString(Path.of("file.txt"), "Hello");
String s = Files.readString(Path.of("file.txt"));

25. ❗ Exception Handling Try Except Finally

Catch and handle runtime errors so programs don’t crash.

Keywords: try, except, catch, finally, raise, throw

Python:

try:
    x = int(input())
except ValueError:
    print("Enter a number")
finally:
    print("Done")

Java:

try {
  int x = Integer.parseInt(s);
} catch (NumberFormatException e) {
  System.out.println("Not a number");
} finally {
  System.out.println("Done");
}

Exceptions: raise (Python) vs throw / throws (Java)

Concept	Python	Java	Keywords
Signal an error	`raise` followed by an exception instance or class	`throw` followed by an exception object	raise, throw
Declare that a method may propagate exceptions	no declaration needed; any exception can be raised	`throws` in method signature lists checked exceptions the method may pass on	throws
Checked vs unchecked	no checked exceptions (runtime enforcement not required)	checked exceptions must be declared with `throws` or handled; unchecked (RuntimeException) need not be declared	checked, unchecked

Python — raise an exception and catch it

def f(x):
    if x <= 0:
        raise ValueError("x must be positive")
try:
    f(0)
except ValueError as e:
    print("Caught:", e)

Java — throw and declare checked exception with throws

void readFile(String path) throws IOException {
    if (path == null) throw new IllegalArgumentException("path null");
    // may throw IOException
}

try {
    readFile(null);
} catch (IOException | IllegalArgumentException e) {
    System.out.println("Caught: " + e);
}

Java — throwing an exception inside a method (checked vs unchecked)

void example() throws IOException {    // declares possible checked exception
    throw new IOException("disk error"); // must be declared or caught
}
void bad() {
    throw new RuntimeException("oops"); // unchecked, no throws required
}

Keywords recap: raise, throw, throws, checked, unchecked.

26. 🔁 Iterators and Generators

Concept	Python (meaning + short snippet)	Java (meaning + short snippet)	Keywords
Iterator	object you can get with `iter()` and advance with `next()`; example below	implement `Iterator<T>` and use `hasNext()` / `next()`; example below	iter, next, hasNext, Iterator
Generator	special iterator(subclass of iterator) created with `yield`, produces values lazily and saves memory	no direct language-level generator; use `Iterator` or Streams for lazy production	yield, lazy, generator

Python — Iterator

it = iter([1,2,3])
print(next(it))  # 1
print(next(it))  # 2

Python — Generator (lazy, memory-efficient)

def nums():
    for i in range(3):
        yield i

for n in nums():
    print(n)  # 0 1 2

Java — Iterator implementation and usage

import java.util.Iterator;
import java.util.NoSuchElementException;

class ArrayIterator<T> implements Iterator<T> {
    private final T[] arr;
    private int i = 0;
    ArrayIterator(T[] arr) { this.arr = arr; }
    public boolean hasNext() { return i < arr.length; }
    public T next() {
        if (!hasNext()) throw new NoSuchElementException();
        return arr[i++];
    }
}

// usage
Integer[] a = {1,2,3};
Iterator<Integer> it = new ArrayIterator<>(a);
while (it.hasNext()) System.out.println(it.next());

Java — lazy alternative using Stream

import java.util.stream.IntStream;
IntStream.range(0,3).forEach(System.out::println); // produces lazily

27. 🧠 Function Copy, Closures, Decorators

Functions are reusable blocks of code. Some languages treat functions as values you can store, pass, or return. Python makes this very easy; Java is more static but can achieve similar effects with objects, interfaces, and lambdas.

Function copying

What it means: Making a reference to a function so you can call it later from another name or place.
Python: Functions are values. Assigning a function to another name makes a copy of the reference, not a new function, and you can call it directly.

  def greet(name):
      return "Hi " + name

  say = greet
  print(say("Ana"))  # Hi Ana

Java: Before Java 8 you used objects implementing an interface. Since Java 8 you can use method references or lambdas stored in variables typed by functional interfaces.

  import java.util.function.Function;

  Function<String,String> greet = name -> "Hi " + name;
  System.out.println(greet.apply("Ana")); // Hi Ana

Closures

What a closure is: A function that "remembers" variables from the place where it was defined even after that place has finished running.
Python: Closures are common and simple: an inner function captures outer variables.

  def make_counter():
      count = 0
      def counter():
          nonlocal count
          count += 1
          return count
      return counter

  c = make_counter()
  print(c())  # 1
  print(c())  # 2

Key idea: counter remembers count.

Java: Lambdas and anonymous classes can capture effectively final variables from the surrounding scope. You cannot reassign captured local variables; to mimic mutable capture you use a holder object (array, AtomicInteger, or field).

  import java.util.function.Supplier;
  import java.util.concurrent.atomic.AtomicInteger;

  Supplier<Integer> makeCounter() {
      AtomicInteger count = new AtomicInteger(0);
      return () -> count.incrementAndGet();
  }

  Supplier<Integer> c = makeCounter();
  System.out.println(c.get()); // 1
  System.out.println(c.get()); // 2

Decorators

What a decorator is (simple): A wrapper that adds behavior to a function without changing its code.
Python (direct feature): Python has a built-in decorator syntax using @. Decorators take a function and return a new function that adds behavior.

  def shout(fn):
      def wrapper(name):
          return fn(name).upper()
      return wrapper

  @shout
  def greet(name):
      return "Hi " + name

  print(greet("Ana"))  # HI ANA

Java (no direct decorator syntax): Java uses patterns and language features to achieve the same goals:
- Use the Decorator design pattern: define an interface, concrete implementation, and decorator classes that wrap implementations.
- Use proxies (dynamic proxies) or annotations + AOP frameworks (Spring) to add behavior around method calls.
- Use higher-order functions (lambdas) and composition for simple function wrapping.

  // Simple decorator pattern example
  interface Greeter { String greet(String name); }

  class BasicGreeter implements Greeter {
      public String greet(String name) { return "Hi " + name; }
  }

  class ShoutDecorator implements Greeter {
      private final Greeter inner;
      ShoutDecorator(Greeter inner) { this.inner = inner; }
      public String greet(String name) { return inner.greet(name).toUpperCase(); }
  }

  Greeter g = new ShoutDecorator(new BasicGreeter());
  System.out.println(g.greet("Ana")); // HI ANA

Quick comparison table

Concept	Python (how it feels)	Java (how to do it)
Function copying	Assign functions to variables; pass/return easily	Use functional interfaces, method references, or objects
Closures	Natural; inner functions capture outer vars and can mutate with nonlocal	Lambdas capture effectively final locals; use holder objects to mutate
Decorators	Native `@decorator` syntax; easy to wrap functions	Use decorator pattern, proxies, or AOP; no built-in `@` for functions

28. 🧊 Final vs Immutable Examples

Prevent modification or reassignment.

Keywords: tuple, immutable, final

Python:

x = (1,2,3)  # immutable tuple

Java:

final int x = 10; // cannot reassign
final class C {}  // cannot extend

29. ❓ What does -> None Colon Ellipsis and void Mean

-> None indicates the function returns nothing (like Java void).
... (ellipsis) is a placeholder used in Protocols or stubs for “no implementation here”.
void (Java) means the method does not return a value. Keywords: -> None, ..., void

class Animal(Protocol):
    def make_sound(self) -> None: ...

void greet() { System.out.println("Hi"); }

30. ✅ Quick Summary and Keywords to Remember

Python is concise and beginner-friendly; Java is explicit and structured. Practice small examples above and revisit keywords. Important keywords: def, class, return, if, else, for, while, try, except, lambda, @staticmethod, static, final, private, public, protected, interface, implements, extends, super(), with, yield, -> None, void.

31.🪄Magic methods

What they are: Python “magic” or dunder methods (names with double underscores) are built-in hooks that let objects behave like language primitives (construction, printing, arithmetic, iteration, context managers, callability, attribute interception). Java achieves the same behaviors with named methods, interfaces, wrapper classes, reflection, or language constructs.

Concept	Python (magic)	Java equivalent / pattern	Quick note
Construction / allocation	new, init	Constructor; JVM allocation (no user new)	Python splits allocation and init; Java uses constructor only
Representation	repr, str	toString()	repr → developer; str → user-friendly
Equality / hashing	eq, hash	equals(Object), hashCode()	Implement both for collections/maps
Ordering	lt, gt, etc.	Comparable.compareTo(T) or Comparator	Python operator hooks vs Java interface
Arithmetic / operators	add, radd, sub, etc.	No operator overloading (except String +); provide add()/mul() methods	Python overloads operators; Java uses named methods
Length / size	len	size() / length	len(obj) → obj.len
Indexing / slicing	getitem, setitem	get(index) / set(index,val) on List or custom methods	Slicing needs custom methods in Java
Membership	contains	contains() on collections	`x in y` → y.contains(x)
Iteration	iter, next (raise StopIteration)	Iterable and Iterator with hasNext()/next()	Python iterator protocol vs Java interfaces
Callable objects	call	Functional interfaces (Function, Supplier) or call()/apply() methods	Python instance()() vs Java lambda or method
Attribute access	getattr, setattr, delattr	Reflection, Map-backed fields, or Proxy (java.lang.reflect.Proxy)	Python dynamic attribute hooks; Java needs explicit mechanisms
Context management	enter, exit (with)	AutoCloseable + try-with-resources	with CM(): → try (CM cm = new CM()) { }
Decorator / wrapper	use wrapper functions and @decorator; wrappers often use call	Decorator design pattern: wrapper classes, proxies, or higher-order functions	Python has syntactic sugar (@); Java uses patterns

Compact examples

Representation / equality (Python)

class P:
    def __init__(self,x): self.x = x
    def __repr__(self): return f"P({self.x})"
    def __eq__(self,other): return isinstance(other,P) and self.x == other.x

Representation / equality (Java)

class P {
  private final int x;
  P(int x){ this.x = x; }
  public String toString(){ return "P(" + x + ")"; }
  public boolean equals(Object o){ return (o instanceof P) && ((P)o).x == this.x; }
  public int hashCode(){ return Integer.hashCode(x); }
}

Iteration (Python)

class Count:
    def __init__(self,n): self.i=0; self.n=n
    def __iter__(self): return self
    def __next__(self):
        if self.i>=self.n: raise StopIteration
        v=self.i; self.i += 1; return v
for v in Count(3): print(v)

Iteration (Java)

import java.util.Iterator;
class Count implements Iterator<Integer> {
  private int i=0, n;
  Count(int n){ this.n=n; }
  public boolean hasNext(){ return i < n; }
  public Integer next(){ return i++; }
}

Context manager (Python)

class CM:
    def __enter__(self): print("enter"); return self
    def __exit__(self, exc_type, exc, tb): print("exit"); return False
with CM(): pass

Try-with-resources (Java)

class CM implements AutoCloseable {
  CM(){ System.out.println("enter"); }
  public void close(){ System.out.println("exit"); }
}
try (CM cm = new CM()) { }

Decorator / wrapper (Python)

def deco(fn):
    def wrapper(*a,**k):
        print("before"); r = fn(*a,**k); print("after"); return r
    return wrapper

@deco
def say(): print("hi")
say()

Decorator-like wrapping (Java)

import java.util.function.Supplier;
Supplier<Void> say = () -> { System.out.println("hi"); return null; };
Supplier<Void> wrapped = () -> {
  System.out.println("before"); say.get(); System.out.println("after"); return null;
};
wrapped.get();

One-line takeaway

Python exposes uniform, language-level dunder hooks for operator and behavior customization; Java maps the same capabilities to named methods, interfaces, design patterns, reflection, or language constructs, but lacks general operator overloading and the uniform dunder dispatch.

Keywords: init, repr, str, add, eq, hash, len, getitem, iter, next, call, getattr, enter, exit, toString, equals, hashCode, Iterable, Iterator, AutoCloseable.

🐍 Python vs ☕ Java — Ordered Beginner’s Guide with Keywords, and Examples

1. 💬 Comments

2. 🔠 Indentation and Code Blocks

3. 🧾 Input Output and Taking Multiple Inputs

4. 🔁 Type Casting Conversions

5. 📦 Variable Types and Basic Data Types

6. ➕ Operators and Conditionals with Comparison Ops

7. 🗝️ Keywords Common Reserved Words

8. 🔍 Conditionals If Elif Else

9. 🔂 Loops For While Nested Loops

10. 🕳️ Pass Statement

11. 📦 Modules Packages Code Organization

12. 🧮 Functions Methods Arguments Multiple Arguments

13. 🔁 Recursion Recursive Functions

14. ⚡ Lambda Functions

15. 🧭 map filter and Streams

16. 🧺 Data Structures

17. 🐾 Classes, Objects, Constructor, Inheritance

🐾 Classes

🧱 Objects

🔧 Constructor

🌱 Inheritance

18. 🔐 Encapsulation ✅ Access Modifiers

19. 🧷 Static Methods and Class vs Instance Variables Examples

20. 🧱 Abstraction Abstract Classes Methods

Abstract classes — simple explanation

21. 🧩 Interfaces vs Protocols Examples

None vs Ellipsis vs Return Nothing

None / null

Ellipsis ... (placeholder)

-> None (Python) vs void (Java)

22. 🦴 Polymorphism Overriding Overloading and super

23. 🔗 Pass by Value vs Reference

24. 📁 File Handling Read Write

25. ❗ Exception Handling Try Except Finally

Exceptions: raise (Python) vs throw / throws (Java)

26. 🔁 Iterators and Generators

27. 🧠 Function Copy, Closures, Decorators

Function copying

Closures

Decorators

Quick comparison table

28. 🧊 Final vs Immutable Examples

29. ❓ What does -> None Colon Ellipsis and void Mean

30. ✅ Quick Summary and Keywords to Remember

31.🪄Magic methods

Compact examples

One-line takeaway

Ellipsis `...` (placeholder)

`-> None` (Python) vs `void` (Java)