Boolean Class

Boolean Class

1. What Is Boolean? (beginner)

boolean = true/false only (no 0/1 like C!). Boolean = wrapper (nullable, storable in lists, parse-able). Conditions, flags, login checks live here!

2. Code — Flags + Parse

boolean pass = true; // primitive (default false if field!)
Boolean obj = Boolean.valueOf("TrUe"); // parse IGNORING case → true!
System.out.println(obj); // true
System.out.println(Boolean.parseBoolean("yes")); // false (only "true" → true!)
System.out.println(Boolean.logicalAnd(true, false)); // false
System.out.println(Boolean.logicalOr(true, false));  // true
// flag pattern (exam!):
boolean loggedIn = false;
// ... after password check ...
loggedIn = true;
if (loggedIn) System.out.println("welcome!");

3. Key Members

Member	Use
Boolean.parseBoolean("true")	String → boolean (case-insensitive, only true→true!)
Boolean.valueOf(...)	object form
Boolean.logicalAnd/Or/Xor(a,b)	explicit logic (no short-circuit confusion!)
obj.booleanValue()	→ primitive

4. Traps

• if (5) / if (1) ERROR (needs boolean! unlike C).
• parseBoolean("yes") = false (NOT error! only "true"→true).
• Boolean null + unbox → NPE: Boolean b = null; if (b) CRASH! (use Boolean.TRUE.equals(b) safe!).

5. Exam Points

• Parse rules + flag program — 3-5 marks, frequent.
• if(5) error + null-unbox NPE — 3 marks, favourite traps.