Side by side

Python ↔ Java

Curated pairs where the two languages solve the same underlying problem in genuinely comparable ways — not a forced mapping between unrelated features. More pairs get added as new topics land.

Identity vs. equality, and reference caching

Python

`is` vs `==`, the small-int cache, and string interning

== compares value (calls __eq__).
is compares identity (same object in memory, same id()).

python

# Python 3.8+ warns on `is` against an int/str literal, since it's almost always a mistake.
# We're deliberately doing it on purpose here to demonstrate identity semantics, so silence that warning.
import warnings
warnings.filterwarnings("ignore", category=SyntaxWarning)

a = 256
b = 256
print("256 is 256:", a is b, "|", a == b)

e = -5
f = -5
print("-5 is -5: ", e is f, "  <- both in the cached range, always True, script or notebook")

Output

256 is 256: True | True
-5 is -5:  True   <- both in the cached range, always True, script or notebook

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Java

`==` vs `.equals()`, and the String constant pool

== on objects compares reference identity. .equals() compares logical equality (as defined by the class). String literals are special: the JVM interns them in a shared constant pool, so two identical literals ARE the same reference — but new String(...) deliberately creates a distinct heap object even if the contents match. .intern() looks a string up in (or adds it to) the pool.

java

String s1 = "hello";
String s2 = "hello";
String s3 = new String("hello");

System.out.println("s1 == s2 (both literals, pooled):      " + (s1 == s2));
System.out.println("s1 == s3 (s3 is `new String(...)`):    " + (s1 == s3));
System.out.println("s1.equals(s3):                         " + s1.equals(s3));
System.out.println("s1 == s3.intern():                     " + (s1 == s3.intern()));

Output

s1 == s2 (both literals, pooled):      true

Output

s1 == s3 (s3 is `new String(...)`):    false

Output

s1.equals(s3):                         true

Output

s1 == s3.intern():                     true

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