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How many types of loops are there in Java?
When should I use a for loop versus a while loop in Java?
What is the difference between a while loop and a do-while loop in Java?
You should loop through the array and use an index / boolean flag to store whether or not the book is found. Then print the message in the end, based on the index / flag value.
int foundAtIndex = -1;
for(int i = 0; i < bookObj.length; i++) {
if(bookObj[i].getName().equals(input)) {
foundAtIndex = i; // store the actual index for later use
break; // no need to search further
}
}
if(foundAtIndex >= 0)
System.out.println("Book Found!");
else
System.out.println("Book not Found!");
Alternatively (unless your assignment specifically requires using an array) you should prefer a Set, which can do the search for you with a single call to contains().
How should I think of it in Object Oriented way?
When looking at a single method, there is not much difference between procedural and OO style. The differences start to appear at a higher level, when trying to organize a bunch of conceptually related data and methods that operate on these.
The OO paradigm is to tie the methods to the data they operate on, and encapsulate both into coherent objects and classes. These classes are preferably representations of important domain concepts. So for your book store, you may want to put all book related code into your Book class. However, the above search method (and the collection of books it operates on) is not related to any particular book instance, so you have different choices:
- put both the collection of books and the search method into
Store(probably as regular members), or - put them into
Bookasstaticmembers.
The first choice is more natural, so I normally would prefer that. However, under specific circumstances the second option might be preferable. In (OO) design, there are hardly ever clean "yes/no" answers - rather tradeoffs between different options, each having their own strengths and weaknesses.
You could introduce state and remember whether you have found the book or not.
If you're not using Java 1.4 or earlier, you could also use the foreach loop syntax:
boolean bookFound = false;
for(Book currentBook : bookObj) {
if(currentBook.getName().equals(input))
//TODO: see above
}
Also, I would suggest looking into the Collections library, and replace your array with a list or set:
Set<Book> books = new HashSet<Book>();
books.put(new Book("Game Over"));
books.put(new Book("Shrek"));
books.put(new Book("Ghost"));
And, while were at it, you could also think about when two books are equal and override equals() and hashCode() accordingly. If equal() would be changed to check the title, you could simply use books.contains(new Book(input)); and have the libraries do the work for you.
The three forms of looping are nearly identical. The enhanced for loop:
for (E element : list) {
. . .
}
is, according to the Java Language Specification, identical in effect to the explicit use of an iterator with a traditional for loop. In the third case, you can only modify the list contents by removing the current element and, then, only if you do it through the remove method of the iterator itself. With index-based iteration, you are free to modify the list in any way. However, adding or removing elements that come before the current index risks having your loop skipping elements or processing the same element multiple times; you need to adjust the loop index properly when you make such changes.
In all cases, element is a reference to the actual list element. None of the iteration methods makes a copy of anything in the list. Changes to the internal state of element will always be seen in the internal state of the corresponding element on the list.
Essentially, there are only two ways to iterate over a list: by using an index or by using an iterator. The enhanced for loop is just a syntactic shortcut introduced in Java 5 to avoid the tedium of explicitly defining an iterator. For both styles, you can come up with essentially trivial variations using for, while or do while blocks, but they all boil down to the same thing (or, rather, two things).
EDIT: As @iX3 points out in a comment, you can use a ListIterator to set the current element of a list as you are iterating. You would need to use List#listIterator() instead of List#iterator() to initialize the loop variable (which, obviously, would have to be declared a ListIterator rather than an Iterator).
Example of each kind listed in the question:
ListIterationExample.java
import java.util.*;
public class ListIterationExample {
public static void main(String []args){
List<Integer> numbers = new ArrayList<Integer>();
// populates list with initial values
for (Integer i : Arrays.asList(0,1,2,3,4,5,6,7))
numbers.add(i);
printList(numbers); // 0,1,2,3,4,5,6,7
// replaces each element with twice its value
for (int index=0; index < numbers.size(); index++) {
numbers.set(index, numbers.get(index)*2);
}
printList(numbers); // 0,2,4,6,8,10,12,14
// does nothing because list is not being changed
for (Integer number : numbers) {
number++; // number = new Integer(number+1);
}
printList(numbers); // 0,2,4,6,8,10,12,14
// same as above -- just different syntax
for (Iterator<Integer> iter = numbers.iterator(); iter.hasNext(); ) {
Integer number = iter.next();
number++;
}
printList(numbers); // 0,2,4,6,8,10,12,14
// ListIterator<?> provides an "add" method to insert elements
// between the current element and the cursor
for (ListIterator<Integer> iter = numbers.listIterator(); iter.hasNext(); ) {
Integer number = iter.next();
iter.add(number+1); // insert a number right before this
}
printList(numbers); // 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
// Iterator<?> provides a "remove" method to delete elements
// between the current element and the cursor
for (Iterator<Integer> iter = numbers.iterator(); iter.hasNext(); ) {
Integer number = iter.next();
if (number % 2 == 0) // if number is even
iter.remove(); // remove it from the collection
}
printList(numbers); // 1,3,5,7,9,11,13,15
// ListIterator<?> provides a "set" method to replace elements
for (ListIterator<Integer> iter = numbers.listIterator(); iter.hasNext(); ) {
Integer number = iter.next();
iter.set(number/2); // divide each element by 2
}
printList(numbers); // 0,1,2,3,4,5,6,7
}
public static void printList(List<Integer> numbers) {
StringBuilder sb = new StringBuilder();
for (Integer number : numbers) {
sb.append(number);
sb.append(",");
}
sb.deleteCharAt(sb.length()-1); // remove trailing comma
System.out.println(sb.toString());
}
}