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Java Forum / General / November 2006boolean bitwise problem
code 1 ====== boolean b1=true; boolean b2=true; System.out.println(b1|b2); what does bitwise operator do for boolean variables...?How it works? N.B Lets look the following piece of code below... byte b1=3; //011 byte b2=2; //010 System.out.println(b1|b2); //011 == 3 so this is basically doing bitwise OR operation,but i am in confusion how it will calculate the similar for boolean type in (code 1),will u please tell how it works? > so this is basically doing bitwise OR operation,but i am in confusion > how it will calculate the similar for boolean type in (code 1),will u have u tried to actually run it? Much like you would except: b1 = true; b2=false; result= true; b1 = false; b2=true; result= true; b1 = true; b2=true; result= true; b1 = false; b2=false; result= false; simple OR regards, Lars Borup Jensen http://www.it-arbejde.dk gk skrev: > code 1 > ====== [quoted text clipped - 15 lines] > how it will calculate the similar for boolean type in (code 1),will u > please tell how it works? > code 1 > ====== [quoted text clipped - 3 lines] > > what does bitwise operator do for boolean variables...?How it works? There is no bitwise | for boolean variables. The symbol "|" is overloaded, representing two different operations: 1. If its operands are integers, it represents their bitwise or. 2. If its operands are booleans, it represents their logical or, true if, and only if, at least one of b1 or b2 is true. Patricia Patricia Shanahan skrev: >> code 1 >> ====== [quoted text clipped - 11 lines] > 2. If its operands are booleans, it represents their logical or, true > if, and only if, at least one of b1 or b2 is true. The difference between || and | is that both operands are evaluated in the single | case, but if the first operand (a) in (a || b) is true, the second operand is not evaluated, which may avoid null references and other side-effects. > Patricia Shanahan skrev: >>> code 1 [quoted text clipped - 17 lines] > second operand is not evaluated, which may avoid null references and > other side-effects. All true, but why drag in "||" when the question was only about "|"? Patricia > All true, but why drag in "||" when the question was only about "|"? Because without that difference in semantics between boolean | boolean and boolean || boolean there is no reason to have a specially overloaded meaning of | for booleans at all. -- chris > > All true, but why drag in "||" when the question was only about "|"? > [quoted text clipped - 4 lines] > there is no reason to have a specially overloaded meaning of | for booleans at > all. And because a lot of poor quality books and courseware, busy or misinformed teachers, etc. continue to go about telling those who try to learn Java that || is for booleans and | is for bitwise/integer operations. Explicit misinformation sometimes needs to be corrected, rather than merely ignored.  SignatureChris Smith > 2. If its operands are booleans, it represents their logical or, true > if, and only if, at least one of b1 or b2 is true. In particular, the difference from || is that || "short-circuits" while | doesn't (it evaluates both boolean expressions). So: "true||isFoo()" will NOT call isFoo(), while "true|isFoo()" will. Same holds for & versus && of course. > > code 1 > > ====== [quoted text clipped - 13 lines] > > Patricia i liked these statements ...point 1 is ok and thats why i gave an byte example for that ....but where from you get the point 2 ? is it in JLS ? your point 2 is probabily a valid explanation...and i guess that from the output .....but i dont see any references anywhere which states something like that ......have you found it anywhere ? >>> code 1 >>> ====== [quoted text clipped - 19 lines] > the output .....but i dont see any references anywhere which states > something like that ......have you found it anywhere ? See the JLS, "15.22.2 Boolean Logical Operators &, ^, and |" http://java.sun.com/docs/books/jls/second_edition/html/expressions.doc.html#5242, "For |, the result value is false if both operand values are false; otherwise, the result is true." Patricia Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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