Java Puzzles

https://jaxenter.com/5-weird-java-questions-that-make-your-head-spin-121270.html

Integer a = 42;

Integer b = 42;

System.out.println(a == b); // yes

Integer c = 666;

Integer d = 666;

System.out.println(c == d);// false

The Integer type keeps a cache of all objects with a value in the range of -128 to 127 for performance reasons. So when you declare new variables in that range, you’re actually referring to the same object.

char ch = '0'; // ASCII for ‘0’ is 48

ch *= 1.1; // 48 x 1.1 is 52.8 which turns to 52 when cast to char

System.out.println(ch); // 52 represents ‘4’ in ASCII

String _‎ = "Hello "; String _‏ = "World"; String _‎‏ = " !!"; System.out.println(_‎+_‏+_‎‏);

Spoiler alert: It prints out “Hello World !!”

How come _, _ and _ are different variables? You might have guessed it right. The answer is with hidden characters that pass on as legit Java identifiers. 

1 2	if (x != (x += 0.0f))     System.out.println("WTF");

You can use any String, and also an int or long of (1 << 24) + 1 works for these types as their respective smallest value. But the smallest value of them all is Double.MIN_VALUE which is rounded to 0.0f when cast to a float.