A Java constructor creates a new instance of an already-defined object. This article discusses how to use Java constructor methods to create a Person object. Note: You need to create two files in the same folder for this example: Person. Let's start by creating a Person class that has four private fields: firstName, lastName, address, and username. These fields are private variables and together their values make up the state of an object.
We've also added the simplest of constructor methods:. The constructor method is similar to any other public method except that it shares the same name as the class, and it cannot return a value. It can have none, one or many parameters. Currently, our constructor method does nothing at all, and it's a good time to consider what this means for the initial state of the Person object.
If you think there's a chance that your object might not be used as you expect and the fields might not be initialized when the object is created, always define them with a default value:.
Normally, to ensure that a constructor method is useful, we would design it to expect parameters. The values passed through these parameters can be used to set the values of the private fields:.
Our constructor method now expects the values of four strings to be passed to it. They are then used to set the initial state of the object. We've also added a new method called displayPersonDetails to enable us to see the state of the object after it has been created. Unlike other methods of an object, the constructor method must be called using the "new" keyword:. Notice how we've switched to the Java main class to call the Person object. When you work with objects, programs will span multiple.
Make sure you save them in the same folder. To compile and run the program, simply compile and run the Java main class file i. The Java compiler is smart enough to realize that you want to compile the Person. The Java compiler gets confused if the parameters of the constructor method have the same names as the private fields.
In this example, you can see that we have distinguished between them by prefixing the parameters with the word "person. We can use the "this" keyword instead:. The "this" keyword tells the Java compiler that the variable to be assigned the value is the one defined by the class, not the parameter.
Price Calculation Based On Quantity
It's a question of programming style, but this method helps us define constructor parameters without having to use multiple names. When designing your object classes, you are not limited to using only one constructor method.
You might decide there are a couple of ways an object can be initialized. The only constraint on using more than one constructor method is that the parameters must differ.
Imagine that at the time we create the Person object, we might not know the username. Let's add a new constructor method that sets the state of the Person object using only the firstName, lastName and address:.
Note that the second constructor method is also called "Person" and it also does not return a value. The only difference between it and the first constructor method is the parameters — this time it expects only three string values: firstName, lastName, and address. Person dave will be created with a firstName, lastName, address, and username. Person jim, however, will not get a username, i. Share Flipboard Email. Paul Leahy. Computer Science Expert.Check out the latest Sales updates!
Learn about the key capabilities and features of Dynamics Sales and experience some of the new features. Download overview guide Watch Sales video. Ace your Dynamics deployment with packaged services delivered by expert consultants.
Dynamics 365 Sales Forum
Explore service offerings. The FastTrack program is designed to help you accelerate your Dynamics deployment with confidence.
Business Applications communities.Please note that we have entered a duplicate entity but it is not displayed in the output. Also, we can directly sort the entries by passing the unordered Set in as the parameter of TreeSet. Now we will see some of the basic operations on the Set i. Union, Intersection and Difference. Union In this, we could simply add one Set with other.
Since the Set will itself not allow any duplicate entries, we need not take care of the common values. Intersection We just need to retain the common values from both Sets.
Difference We just need to remove all the values of one Set from the other. Expected Output:. This article is contributed by Pranjal Mathur. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute geeksforgeeks. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
Code Review Stack Exchange is a question and answer site for peer programmer code reviews. It only takes a minute to sign up. I am thinking about how an inventory could be designed. The requirements for this inventory will be the following:. Now of course there are some issues with this implementation.
But the thing that worries me the most is the fact that Item has quantity as a field. Is that considered bad design? If quantity was not a field in item then I guess Inventory would have an ArrayList of items, and increaseQuantity would invoke items. But then, isn't it pointless to have duplicate items in an ArrayList when all you need to know is what kind of items you have and in what quantity? The reason is that it is the wrong abstraction. If you pick up and hold ten pebbles in your hand, the number ten is a property of your hand because it is how many things it is holdingnot the pebble which is just a pebble.
Consider if you drop all the pebbles, now the quantity of pebbles in your hand changes to 0. But if the quantity was a property of the pebble, and you dropped all the pebbles how would you model that would each of the pebbles have a quantity of 0 now?
What if you hand the pebbles over to some one else? Then you would change the quantity in respective hand, but if the quantity was part of the pebble you couldn't model this transaction at all. Similarly the quantity should be a property of the inventory how many of X does it containnot of the Item which is just an item. Somehow this makes me think of Database Normal Forms.
Simply have a Map with Item as key and an Integer quantity as value. This solves your duplicate items problem as well. Note that you will need to implement equals and hashCode for Item. Sign up to join this community. The best answers are voted up and rise to the top.
Home Questions Tags Users Unanswered. Inventory of objects with item types and quantities Ask Question. Asked 3 years, 4 months ago.
Active 3 years, 4 months ago. Viewed 9k times. The requirements for this inventory will be the following: There will be predefined item types in the inventory.
The user can define new item types and add them to the inventory.The Set interface places additional stipulations, beyond those inherited from the Collection interface, on the contracts of all constructors and on the contracts of the addequals and hashCode methods. Declarations for other inherited methods are also included here for convenience. The specifications accompanying these declarations have been tailored to the Set interface, but they do not contain any additional stipulations.
The additional stipulation on constructors is, not surprisingly, that all constructors must create a set that contains no duplicate elements as defined above. Note: Great care must be exercised if mutable objects are used as set elements. The behavior of a set is not specified if the value of an object is changed in a manner that affects equals comparisons while the object is an element in the set.
A special case of this prohibition is that it is not permissible for a set to contain itself as an element. Some set implementations have restrictions on the elements that they may contain. For example, some implementations prohibit null elements, and some have restrictions on the types of their elements.
Attempting to add an ineligible element throws an unchecked exception, typically NullPointerException or ClassCastException. Attempting to query the presence of an ineligible element may throw an exception, or it may simply return false; some implementations will exhibit the former behavior and some will exhibit the latter.
More generally, attempting an operation on an ineligible element whose completion would not result in the insertion of an ineligible element into the set may throw an exception or it may succeed, at the option of the implementation.
Such exceptions are marked as "optional" in the specification for this interface. This interface is a member of the Java Collections Framework. Since: 1.
ObjectCollections. Object  toArray Returns an array containing all of the elements in this set. If this set contains more than Integer. The elements are returned in no particular order unless this set is an instance of some class that provides a guarantee.
If this set makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array will be "safe" in that no references to it are maintained by this set.
In other words, this method must allocate a new array even if this set is backed by an array. The caller is thus free to modify the returned array. This method acts as bridge between array-based and collection-based APIs. If the set fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this set. If this set fits in the specified array with room to spare i.
This is useful in determining the length of this set only if the caller knows that this set does not contain any null elements. Like the toArray method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.
I'm looking for suggestions, improvements and comments about Object oriented approach, style, readability or anything else. The class design is not so good.
For example, why does an item have a quantity property?
No, quantity is the property of your shopping basket, not the milk. I made the constructor protected. The reason is that you have a requirement to ensure unique codes. That's a form of instance controland a common way to implement is the factory pattern. So I suggest to create an ItemFactory class with a public createItem method that can create Item objects, and keep track of their codes in a Mapto check and prevent duplicates.
Finally, make sure that all classes have one clear responsibility. For example, if the main responsibility of the Shop class is to manage the inventory items and their quantitiesthen it should not have the responsibility of parsing user input from the console.
That responsibility should go to another class. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. ArrayList for Shop implementatin Ask Question. Asked 5 years, 5 months ago. Active 1 year, 3 months ago. Viewed 10k times. Time to time rate of the items may change.
Whenever an item is issued or received existence of the item is checked and quantity is updated. In case of issue, availability of quantity is also to be checked.
Find how many items cost more than a given amount. The amount will be a parameter. ItemDemo class containing main method package items; import java. Add items to list" ; System. Issue item" ; System. Update item list" ; System. Display item details" ; System. Check price for a item" ; System. Exit" ; System. ArrayList; import java. InputMismatchException; import java. Iterator; import java.Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
Use the Graphics2D class rendering hints attribute to specify whether you want objects to be rendered as quickly as possible or whether you prefer that the rendering quality be as high as possible. To set or change the rendering hints attribute in the Graphics2D context, construct a RenderingHints object and pass it into Graphics2D by using the setRenderingHints method.
If you just want to set one hint, you can call Graphics2D setRenderingHint and specify the key-value pair for the hint you want to set. The key-value pairs are defined in the RenderingHints class. For example, to set a preference for antialiasing to be used if possible, you could use setRenderingHint :. All rights reserved. Hide TOC. Advanced Topics in Java2D.
Constructing Complex Shapes from Geometry Primitives.
Controlling Rendering Quality
Values should be a positive integer in the range to A lower value eg corresponds to higher contrast text when displaying dark text on a light background. A higher value eg corresponds to lower contrast text when displaying dark text on a light background.
A typical useful value is in the narrow range If no value is specified, a system or implementation default value will be applied.