The for-in Loop in Java

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The for-in Loop

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I only want to talk about the for-in loop here for the sake of context You will see a proper discussion of it in 5, when we talk about classes and objects For now, think of an object as a tool chest that contains a bunch of tools The for-in loop will extract each tool individually from that tool chest, and allow you to examine and manipulate it on its own In the following code, we create a simple object (compatible with JavaScript 15) and retrieve each of its properties using the for-in loop

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<html> <head> <title>JavaScript Test</title>

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CHAPTER 2: Learn JavaScript Fundamentals

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</head> <body> <h1>for-in Loop</h1> <script language="JavaScript" type="text/javascript">  </script> </body> </html>

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This program creates an object named toolchest The object is created using an object literal, as discussed in 5

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// We define the tool chest object var toolchest = {tool1:"Wrench", tool2:"Hammer", tool3:"Cordless drill", tool4:"Needlenose pliers"};

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The code that we re interested in is the for-in loop:

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// for-in iterates over its properties for (var tool in toolchest) { documentwrite(toolchest[tool] + "<BR>"); }

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This code picks loops through the contents of the toolchest object tool1, tool2, tool3, and tool4 When executed, the program outputs the value of each property, like so

The break and continue Statements

We already saw the break statement in action when we looked at the switch statement When JavaScript encounters a break statement inside a switch, it stops executing code inside the switch and continues execution at the first statement that follows it The break statement works in a similar fashion with loops When JavaScript encounters a break statement, it stops executing the code inside the loop and starts again at the first statement outside the loop The break statement is not valid outside a loop or a switch statement The continue statement causes JavaScript to stop executing code inside the loop as well, but execution continues at the next iteration of the loop instead In effect, the break statement says, Exit the loop, while the continue statement says, Skip this iteration and move on to the next The continue statement is also not valid outside of a loop

var Fahrenheit, Celsius; for (Celsius = -70; Celsius <= 70; Celsius += 10) { Fahrenheit = (Celsius * 9/5) + 32; documentwrite ("Celsius = " + Celsius); documentwrite (", Fahrenheit = " + Fahrenheit + "<br>"); if (Fahrenheit > 100) { // It's getting hot in here break; } }

CHAPTER 2: Learn JavaScript Fundamentals

The for loop in this code is designed to run through all of the degrees Celsius starting at 70, incrementing by 10 degrees per iteration, until Celsius reaches +70 degrees ( 70, 60, 50, 40, etc) But if you examine the code inside the loop, it tells JavaScript to break out of the loop when the temperature exceeds 100 Fahrenheit Since 100 Fahrenheit is approximately 37 Celsius, the loop will actually exit when Celsius hits 40, and not 70 The break statement causes the loop to exit prematurely

The continue statement is very useful when you want to loop through a range of values, ignoring some that don t meet certain criteria But when you find some that do, you have a lot of code to execute inside the loop Instead of surrounding dozens of lines of code with a giant if statement, the continue statement can be used to skip on to the next iteration

// Which numbers are evenly divisible by 23 var iNumber; for (iNumber = 1; iNumber <= 1000; iNumber++) { if (iNumber % 23 > 0) { // Not divisible by 23 continue; } documentwrite("<b>" + iNumber + "</b>"); documentwrite(" is evenly divisible by 23!<br>"); }

The for-in Loop in Java Drawer QR Code in Java The for-in Loop

The for-in Loop in Java

Drawer QR Code in Java The for-in Loop