Part I: Building Killer Web Pages for Fun and Profit The for-in loop in Java

Creation Quick Response Code in Java Part I: Building Killer Web Pages for Fun and Profit The for-in loop

If you like for, you ll love the for-in loop You use the for-in loop for looping, or iterating, through all properties of an object, like so:

for (var in object) { statements }

As an example, here s a function that you can use to loop through all properties of a given object and display each property s name and associated value:

function displayProperties(inputObject, inputObjectName){ var result = for (var eachProperty in inputObject) { result += inputObjectName + + eachProperty + = + inputObject[eachProperty] + <BR> } return result }

This code might appear confusing at first, but it s pretty straightforward when you understand what the for-in loop does: 1 The code declares a function called displayProperties() that accepts two arguments: inputObject and inputObjectName Here s one way to call this function:

documentwriteln(displayProperties(document, document ))

2 The JavaScript interpreter hops up to the displayProperties() definition, only this time it substitutes the document object for the argument inputObject and substitutes the document string for the argument inputObjectName 3 Inside the for-in loop, the JavaScript interpreter loops through all properties of the document object Each time it comes to a new property, the interpreter assigns the new property to the eachProperty variable Then the interpreter constructs a string and adds the string to the end of the result variable After the for-in loop has looped through all properties of the document object, the result variable holds a nice long string containing the names and values of all properties in the document object (For the skinny on objects, flip to 4)

Displaying (or dumping, as it s called in programmerese) the property values of an object can be useful when you re trying to track down an error in your script A method like documentwriteln() enables you to know exactly what the interpreter thinks objects look like (which is sometimes quite different from the way you think they look) Take a look at the ch3_forinhtm file to see an example of the for-in loop

The while loop s job is to do something that is, to execute one or more JavaScript statements while some programmer-defined condition is true Obviously, then, you want to make sure that one of the statements in the body of your while loop changes the while condition in some way so that at some point it becomes false Here s the generic version of the while loop

while (condition) { statements }

var totalInventory=700 var numberPurchased=200 var numberSales=0 while (totalInventory > numberPurchased) { totalInventory = totalInventory - numberPurchased numberSales++ } documentwriteln( Our stock supply will support + numberSales + of these bulk sales )

Step into the JavaScript interpreter s virtual shoes for a minute and take a look at how this all works! (Remember, you re the JavaScript interpreter now, so be serious) While the total inventory is more than the number purchased Well, 700 is greater than 200 Okay Subtract the number purchased from the total inventory and bump up the number of sales by 1 Number of sales is now 1 That s one loop down While the total inventory is more than the number purchased Hmm Total inventory is 500 now, and that s still greater than 200, so I need to subtract the number purchased from the total inventory and add another 1 to the number of sales Number of sales is now 2 Two loops down

While the total inventory is more than the number purchased Okay, total inventory is 300 now, which is still greater than 200 Subtract number purchased from total inventory, add 1 to the number of sales Number of sales is now 3 Three loops down While the total inventory is more than the number purchased Hey! It s not! Total inventory is 100, and the number purchased is 200 I m outta here Here s what I ll write to the screen: Our stock supply will support 3