CODEWITHSUNDEEP
javaloopsfor-loopforeach
JAN
JAN

Reputation: 21865

For loop in the form of : "for (A b : c)" in Java

This is the first time that I've seen this kind of syntax : 

// class Node
public class Node { 

...
...

}

public class Otherclass { ... }

Otherclass graph = new Otherclass();

// getSuccessors is a method of Otherclass class 

Node currentNode ;

List<Node> successors = graph.getSuccessors(currentNode);

// weird for loop 

for (Node son : successors) { 

// do something 

}

What is that for loop ? some kind of a Matlab syntax ?

Is there any other way to write that for loop ?

Regards

Upvotes: 5

Views: 32188

Answers (7)

someone
someone

Reputation: 6572

This is one representation of your for loop

for(int i=0;i<successors.size();i++){

        Node myNode = successors.get(i);
    }

This is not a for loop but still you could do this.

Iterator<Node> itr = successors.iterator();

    while(itr.hasNext()){
        Node myNode = itr.next();
        // your logic
    }

Upvotes: 2

Anirudh Ramanathan
Anirudh Ramanathan

Reputation: 46728

That is a for-each loop (also called an enhanced-for.)

for (type var : arr) { //could be used to iterate over array/Collections class
    body-of-loop
}

The basic for loop was extended in Java 5 to make iteration over arrays and other collections more convenient. This newer for statement is called the enhanced for or for-each

(Documentation)

Upvotes: 10

Sleiman Jneidi
Sleiman Jneidi

Reputation: 23329

it is called enhanced for loop, instead of using iterator to iterate over a collection you can simply use this for loop

using iterators

Iterator<String> i=a.iterator();

while(i.hasNext())
{
String s=i.next();
}

you can simply use the enhanced for loop.

for(String s : a)
{
 .. do something
}

so it is just a syntactic sugar introduced in Java 5, that do the same functionality of the iterators and it uses the iterator internally. The class should implement the Iterator interface in order to use this for loop

class Node<T> implements Iterator<String>{

@Override
public boolean hasNext() {
    // TODO Auto-generated method stub
    return false;
}

@Override
public String next() {
    // TODO Auto-generated method stub
    return null;
}

@Override
public void remove() {
    // TODO Auto-generated method stub

}



}

Upvotes: 1

Rohit Jain
Rohit Jain

Reputation: 213223

It is called Enhanced for-loop. It basically iterates over a Collection by fetching each element in sequence. So you don't need to access elements on index.

List<Integer> list = new ArrayList<Integer>();

for (int val: list) {
    System.out.println(val);  // Prints each value from list
}

See §14.14.2 - Enhanced for loop section of Java Language Specification.

Upvotes: 3

hmjd
hmjd

Reputation: 121971

It is the enhanced for statement. See section 14.14.2. The enhanced for statement of the Java Language Specification.

Upvotes: 4

Anthony Grist
Anthony Grist

Reputation: 38345

It's a for each loop. You could also write it like this:

for(int i = 0; i < successors.size(); i++) {
    Node son = successors.get(i);
}

Though the only time I'd personally do that is when the index is needed for doing something other than accessing the element.

Upvotes: 7

gefei
gefei

Reputation: 19766

it means "for each son in successors, where the type of son is Node"

Upvotes: 2

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