Double Class

Double Class

1. Why Double Is Default (beginner)

double = 8-byte decimal, Java's default for 3.14 (no suffix needed!). Double = wrapper. Use for marks average, science, geometry — everywhere decimals needed (unless memory-critical float!).

2. Code — Average Done Right + Parse

int total = 7, n = 2;
System.out.println(total / n);        // 3 (int trap!)
System.out.println(total / 2.0);      // 3.5 (double math!)
Double obj = Double.valueOf("3.14");  // parse
System.out.println(obj + 1);          // 4.14 (unboxed!)
System.out.println(Double.MAX_VALUE); // 1.7976931348623157E308
// precise compare (never ==!):
double a = 0.1 + 0.2;
System.out.println(Math.abs(a - 0.3) < 0.0001); // true (epsilon trick!)

3. Key Members

Member	Use
Double.parseDouble("3.14")	String → double (CLI decimal args!)
Double.isNaN(x) / isInfinite(x)	check 0.0/0, 1.0/0
Double.compare(a,b)	safe compare (-1/0/1, handles NaN!)
Double.valueOf(...)	object form for lists

4. Traps

• == fails on decimals (0.1+0.2 != 0.3 binary!). Use epsilon or compare.
• Double(null) unbox → NPE. Parse garbage → NumberFormatException.
• 1/0 (int) crashes (ArithmeticException); 1.0/0 (double) = Infinity!

5. Exam Points

• Average fix + epsilon + parse — 5 marks, frequent.
• int-divide crash vs double Infinity — 3 marks, favourite contrast.