Foreach loop in java

Is there a way in Java's for-each loop for(String s : stringArray) the only way to have such a counter available in a for-each loop? No, but you can provide your own counter. The reason for this is that the for-each loop internally does not have a counter; it is based on the Iterator to loop through the "collection" - which may not be a collection at all, and may in fact be something not at all based on indexes (such as a linked list). Why can't we maintain an index/counter for anything which is Iterable? LinkedList is not based on indexes but we still have ListIterator which maintains a counter internally while iterating on it. If we are iterating on something that means we have n number of items, be it any format/DS. Isn't it? Any example where an index can't be maintained will be helpful. Thanks. There is another way. Given that you write your own Index class and a static method that returns an Iterable over instances of this class you can for (Index each: With.index(stringArray)) @mR_fr0g don't worry, I benchmarked this and creating all these objects is not any slower than reusing the same object for each iteration. The reason is that all these objects are allocated in eden space only and never life long enough to reach the heap. So allocating them is as fast as e.g. allocating local variables. @akuhn Wait. Eden space does not mean that no GC is reaquired. Quite the opposite, you need to invoke constructor, scan sooner with GC and finalize. This not only loads CPU bu...

Looping through a collection of objects and doing something with each object is one of the most common programming idioms a Java developer can face. You’ve no doubt coded such loops many times. The following sample shows how to iterate over an array with a for loop in Java: List names = new ArrayList(); names.add("a"); names.add("b"); names.add("c"); for (Iterator it = names.iterator(); it.hasNext(); ) Note that the Iterator, the List reference, and the ArrayList are all bound to the Product type. Once you have implemented the java.lang.Iterable interface, client code can use the foreach loop. Here is a bit of example code: Catalog catalog = new Catalog(); catalog.add(new Product("1", "pinto", new BigDecimal("4.99"))); catalog.add(new Product("2", "flounder", new BigDecimal("64.88"))); catalog.add(new Product("2", "cucumber", new BigDecimal("2.01"))); for (Product product: catalog) product.discount(new BigDecimal("0.1")); for (Product product: catalog) System.out.println(product); Summary of How to Use Java foreach Loops The foreach loop provides a simple, consistent solution for iterating arrays, collection classes, and even your own collections. It eliminates much of the repetitive code that you would otherwise require. The foreach loop eliminates the need for casting as well as some potential problems. The foreach loop is a nice new addition to Java that was long overdue. I greatly appreciate the added simplicity in my source code. Jeff Langr is a freelance author and ...

A loop is a control statement which executes a particular block of code repeatedly until a given condition becomes false. There are various types of loops such as while, do-while and for loop. In this article, we will be focusing on for loop and its enhanced version. If you’re looking for forEach method introduced in Java 8: Difference between For and For-each Loop in Java For Loop Foreach Loop It uses an index of an element to fetch data from an array It uses an iteration variable to automatically fetch data from an array Termination of this traditional loop is controlled by loop condition. Therefore, For loop executes repeatedly until the given condition turns out to be false No such provision is provided in foreach, instead break statement can be used to terminate the execution of the loop early, otherwise, it executes until the last element gets evaluated It requires loop counter, initial and end values, in order to iterate through all the elements of an array It automates the iteration by using the iteration variable which stores one element each time When we iterate through using traditional for loop we can manipulate the actual data of an array The iteration variable in foreach is read-only. It means changes made on iteration value would not affect the actual data of the collection or array It was introduced in Java 1 It was introduced back in Java 5 It has the flexibility of the iterating an array whether it is increasing order or decreasing order It can iterate on...

Java For-each Loop | Enhanced For Loop The Java for-each loop or enhanced for loop is introduced since J2SE 5.0. It provides an alternative approach to traverse the array or collection in Java. It is mainly used to traverse the array or collection elements. The advantage of the for-each loop is that it eliminates the possibility of bugs and makes the code more readable. It is known as the for-each loop because it traverses each element one by one. The drawback of the enhanced for loop is that it cannot traverse the elements in reverse order. Here, you do not have the option to skip any element because it does not work on an index basis. Moreover, you cannot traverse the odd or even elements only. But, it is recommended to use the Java for-each loop for traversing the elements of array and collection because it makes the code readable. Advantages • It makes the code more readable. • It eliminates the possibility of programming errors. Syntax The syntax of Java for-each loop consists of data_type with the variable followed by a colon (:), then array or collection. for(data_type variable : array | collection) How it works? The Java for-each loop traverses the array or collection until the last element. For each element, it stores the element in the variable and executes the body of the for-each loop. For-each loop Example: Traversing the array elements import java.util.*; class ForEachExample2 Output:

Student's names(String[]) and corresponding marks(int[]) are stored in different arrays. How may I iterate over both arrays together using for each loop in Java ? void list() One trivial way could be using index variable in the same loop. Is there a good way to do? These two arrays are working in parallel, and their only association is via the index (so you can't use an enhanced for loop because you need to know the index). Stefan rightly points out this is very bad design that offers so little flexibility I don't think it's ever used outside of arbitrary examples. You need to do it using the regular for loop with an index, like this: if (marks.length != studentNames.length) The underlying problem is actually that you should tie both of the arrays together and iterate across just one array. Here is a VERY simplistic demonstration - you should use getters and setters and you should also use a List instead of an array but this demonstrates the point: class Student

The for loop defines three types of statements separated with semicolons. The first statement is the initialization statement. The second one defines the termination condition. The last statement is the update clause. Here we’re simply using an integer variable as an index: for (int i = 0; i < countries.size(); i++) In the initialization, we must declare an integer variable to specify the starting point. This variable typically acts as the list index. The termination condition is an expression that returns a boolean after evaluation. Once this expression evaluates to false, the loop finishes. The update clause is used to modify the current state of the index variable, increasing it or decreasing it until the point of termination. The enhanced for loop is a simple structure that allows us to visit every element of a list. It's similar to the basic for loop, but more readable and compact. Consequently, it's one of the most commonly used forms to traverse a list. Notice that the enhanced for loop is simpler than the basic for loop: for (String country : countries) 3. Iterators An Iterator is a design pattern that offers us a standard interface to traverse a data structure without having to worry about the internal representation. This way of traversing data structures offers many advantages, among which we can emphasize that our code doesn't depend on the implementation. Therefore, the structure can be a binary tree or a doubly linked list, since the Iterator abstracts us f...

• v • t • e In foreach loop (or for-each loop) is a foreach is usually used in place of a standard for loop constructs, however, foreach loops x times". This avoids potential The foreach statement in some languages has some defined order, processing each item in the collection from the first to the last. The foreach statement in many other languages, especially Syntax [ ] Syntax varies among languages. Most use the simple word for, roughly as follows: for each item in collection: do something to item Language support [ ] ActionScript 3.0 [ ] for each .. in for Obj of X loop -- Work on Obj end loop ; C [ ] The However, two obvious problems occur: • The macro is unhygienic: it declares a new variable in the existing scope which remains after the loop. • One foreach macro cannot be defined that works with different collection types (e.g., array and linked list) or that is extensible to user types. C string as a collection of char #include /* foreach macro viewing a string as a collection of char values */ #define foreach(ptrvar, strvar) \ char* ptrvar; \ for (ptrvar = strvar; (*ptrvar)!= '\0'; *ptrvar++) int main ( int argc , char ** argv ) C int array as a collection of int (array size known at compile-time) #include /* foreach macro viewing an array of int values as a collection of int values */ #define foreach(intpvar, intarr) \ int* intpvar; \ for (intpvar = intarr; intpvar < (intarr + (sizeof(intarr)/sizeof(intarr[0]))); ++intpvar) int main ( int argc , char ** argv )...

There are various ways by which we can iterate through the HashTable which are as follows: • Using Enumeration Interface • Using keySet() method of Map and Enhance for loop • Using keySet() method of Map and Iterator Interface • Using entrySet() method of Map and enhanced for loop • Using entrySet() method of Map and Iterator interface • Using Iterable.forEach() method from version Java 8 Now let us discuss the internal implementation of all methods one by one in detail to get a better understanding of iteration through HashTable Method 1: Using Enumeration Interface java.util.Enumeration interface is one of the predefined interfaces, whose object is used for retrieving the data from collections framework variable. In a forward direction only and not in the backward direction. This interface has been superseded by an iterator. Rank : 5 Name : Piyush Rank : 4 Name : Hritik Rank : 3 Name : Bijay Rank : 2 Name : Shyam Rank : 1 Name : Ram Method 2: Using keySet() method of Map and Enhance for loop The java.util.HashMap.keySet() method in Java is used to create a set out of the key elements contained in the hash map. It basically returns a set view of the keys, or we can create a new set and store the key elements in them. Output Rank : 5 Name : R Rank : 4 Name : Pearl Rank : 3 Name : Python Rank : 2 Name : Scala Rank : 1 Name : Java Method 3: Using keySet( ) method of Map and Iterator Interface Again we will be using the same method as been implemented in the above example but...