Java Puzzlers презентация

Java Puzzlers From the book Java Puzzlers by Joshua Bloch and Neal Gafter

Oddity The following method tests whether its argument is odd: public static boolean isOdd(int i) { return i % 2 == 1; } Does it work? It gives the correct answer for ¾ of the integers

Making change public class Change { public static void main(String[] args) { System.out.println(2.00 - 1.10); } } 0.8999999999999999

Long Division public class LongDivision { public static void main(String[] args) { final long MICROS_PER_DAY = 24 * 60 * 60 * 1000 * 1000; final long MILLIS_PER_DAY = 24 * 60 * 60 * 1000; System.out.println(MICROS_PER_DAY / MILLIS_PER_DAY); } } 5

Addition public class Addition { public static void main(String[] args) { System.out.println(12345 + 5432l); } } 17777

Tweedledum Declare variables x and i such that x += i; is legal, but x = x + i; is not legal short x = 0; int i = 123456;

Tweedledee Declare variables x and i such that x = x + i; is legal, but x += i; is not legal Object x = "Hello "; String i = "world!";

+= public class PlusEquals { public static void main(String[] args) { int i = 2; i += 3.75; System.out.println(i); } } 5

Last Laugh public class LastLaugh { public static void main(String[] args) { System.out.print("H" + "a"); System.out.print('H' + 'a'); } } Ha169

Indecision public class Indecisive { public static void main(String[] args) { System.out.println(decision()); } static boolean decision() { try { return true; } finally { return false; } } } false

HelloGoodbye public class HelloGoodbye { public static void main(String[] args) { try { System.out.println("Hello world!"); System.exit(0); } finally { System.out.println("Goodbye world!"); } } } Hello world!

The reluctant constructor public class Reluctant { private Reluctant internalInstance = new Reluctant(); public Reluctant() throws Exception { throw new Exception("I'm not coming out!"); } public static void main(String[] args) { try { Reluctant b = new Reluctant(); System.out.println("Surprise!"); } catch (Exception e) { System.out.println("I told you so."); } } } Exception in thread "main" java.lang.StackOverflowError

Hello again public class Null { public static void main(String[] args) { ((Null)null).greet(); } public static void greet() { System.out.println("Hello world!"); } } Hello world!

The End