1. The for-each or for-all loop introduced in Java 5
The New For Loop
The for-each or for-all loop introduced in Java 5
Copyright © Curt Hill

2. The Old For The for loop is essentially the same as that of C and C++
Not changed since early 1970s
It is a counting loop, where you show three things:
Where to start counting
Where to end counting
What to count by
Sometimes that is not so easy
Copyright © Curt Hill

3. Collections
There are a number of collections where it is not so easy to infer
These include:
pixels in a picture
items in an array
items in one of many Java data structures
The new for is designed to access each one without having to know how many there are
Copyright © Curt Hill

4. The New For The new for infers those three things
It must infer them given a situation
In the next screen we will consider how to do this with a counting for
Copyright © Curt Hill

5. Old picture processing
Consider one way to do this: static void process (Picture p){ Pixel [] px = p.getPixels(); int len = px.length; for(int i = 0;i<len;i++){ Pixel ap = px[i]; ap.setRed(0); } // end of for } // end of method
Copyright © Curt Hill

6. New picture processing
Now we do it with the new for Picture p … ; Pixel [] px = p.getPixels(); for(Pixel ap: px){ // process ap }
The variable ap represents the pixel and may be processed
This variable has scope only in the for loop
Copyright © Curt Hill

7. Inferring
The Java compiler examines the array for the questions of the old for
Where to start: Arrays always start at zero
Where to end: Arrays contain a length
What to count by: Make sure each one is touched
Copyright © Curt Hill

8. The Form of the For The form is different: for(type var : object)
Where
type is the type of array object
var is the name of the one item that the body will work on
object is the original array name
Variable var will receive the values from the array
Notice that there is nothing like a subscript or subscripting
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9. Picture processing again
The new for does nothing that the old did not do Picture p … ; Pixel [] px = p.getPixels(); for(Pixel ap: px){ // process ap }
Now we infer the start and end subscripts
The subscripting is hidden from us
Copyright © Curt Hill

10. Iteration This for is actually an iterator
It will walk through any kind of data structure and touch each item
Even if that data structure is not linear
Arrays are linear
Trees are not
Fortunately, we do not have to worry about this during this semester
Copyright © Curt Hill

11. In Conclusion For picture processing we can use either
Sometimes that may not be the case
Counting for explicitly shows the initialization, test and advancement
For all infers them all
May only be used with container objects
The only container we will see this semester is the array, but others exist
Copyright © Curt Hill