Using the Keyword Final with Inheritance in Java

While one of Javas strengths is the concept of inheritance, in which one class can derive from another, sometimes its desirable to prevent inheritance by another class. To prevent inheritance, use the keyword final when creating the class. For example, if a class is likely to be used by other programmers, you may wish to prevent inheritance if any subclasses created could cause problems. A typical example is the String class. If we wanted to create a String subclass: public class MyString extends String{ï » ¿} We would be faced with this error: cannot inherit from final java.lang.String The designers of the String class realized that it was not a candidate for inheritance and have prevented it from being extended. Why Prevent Inheritance? The main reason to prevent inheritance is to make sure the way a class behaves is not corrupted by a subclass. Suppose we have a class Account and a subclass that extends it, OverdraftAccount. Class Account has a method getBalance(): public double getBalance(){ return this.balance; } At this point in our discussion, subclass OverdraftAccount has not overridden this method. (Note: For another discussion using this Account and OverdraftAccount classes, see how a subclass can be treated as a superclass). Lets create an instance each of the Account and OverdraftAccount classes: Account bobsAccount new Account(10); bobsAccount.depositMoney(50); OverdraftAccount jimsAccount new OverdraftAccount(15.05,500,0.05); jimsAccount.depositMoney(50); //create an array of Account objects //we can include jimsAccount because we //only want to treat it as an Account object Account[] accounts {bobsAccount, jimsAccount}; //for each account in the array, display the balance for (Account a:accounts) { System.out.printf(The balance is %.2f%n, a.getBalance()); } The output is: The balance is 60.00 The balance is 65.05 Everything appears to work as expected, here. But what if OverdraftAccount overrides the method getBalance()? There is nothing to prevent it from doing something like this: public class OverdraftAccount extends Account { private double overdraftLimit; private double overdraftFee; //the rest of the class definition is not included public double getBalance() { return 25.00; } } If the example code above is executed again, the output will be different because the getBalance() behavior in the OverdraftAccount class is called for jimsAccount: The output is: The balance is 60.00 The balance is 25.00 Unfortunately, the subclass OverdraftAccount will never provide the correct balance because we have corrupted the behavior of the Account class through inheritance. If you design a class to be used by other programmers, always consider the implications of any potential subclasses. This is the reason the String class cannot be extended. Its extremely important that programmers know that when they create a String object, its always going to behave like a String. How to Prevent Inheritance To stop a class from being extended, the class declaration must explicitly say it cannot be inherited. This is achieved by using the final keyword: public final class Account { } This means that the Account class cannot be a superclass, and the OverdraftAccount class can no longer be its subclass. Sometimes, you may wish to limit only certain behaviors of a superclass to avoid corruption by a subclass. For example, OverdraftAccount still could be a subclass of Account, but it should be prevented from overriding the getBalance() method. In this case use, the final keyword in the method declaration: public class Account { private double balance; //the rest of the class definition is not included public final double getBalance() { return this.balance; } } Notice how the final keyword is not used in the class definition. Subclasses of Account can be created, but they can no longer override the getBalance() method. Any code calling that method can be confident it will work as the original programmer intended.

International Energy Resources And Prices - 1259 Words

1. In what ways is OPEC important, and not so important, in terms of international energy resources and prices? In the panorama of international relations, the absence of universal or potentially universal institution dealing with energy is notable. Established in 1960, OPEC’s original trigger was the continuing slide in posted prices, which at the time were unilaterally established by the International Oil Companies. It is frequently maintained that OPEC is a cartel that has the power to effectively limit its members’ oil production and exports and thus influence oil prices. However, this representation is way off the mark, and grossly exaggerates OPEC’s cohesion and influence. In actual fact, OPEC is more akin to a club whose members†¦show more content†¦By that, the major pro will be a cleaner air and better quality, reducing the number of deaths caused by poor quality air. The con of fracking for health problems is that air quality dynamics around fracking operations are not fully understood. Similarly, fracking is known for its low water intensity compared to fuels and nuclear, which use up to 10 times more water than fracking (per energy unit). However, the con is the intrusive presence of fracking within the environment where it is implemented: noise, heavy infrastructures etc. In addition, fracking raises the question of greenhouse gas leaks. The major pro of hydraulic fracturing here is the gigantic benefit of release of green house emission: it is commonly believed that natural gas produces only about 50% of the greenhouse gas emission compared with burning of coal. On the other hand, researches have showed that big quantities of methane, a powerful greenhouse gas, have leaked from fracking. The third important point linked to hydraulic fracturing concerns drinking water and shallow aquifers. The major pro raised in that question is the reliability of fracking operations and infrastructures: drinking water is situated at different level than oil or gas which means that with an efficient good quality piping system, contaminating drinking water supplies is very unlikely. However, this particular point has revealed to be a

Analysis Of Hills Like White Elephants And The Man...

Reading, whether it is a short story, newspaper, or novel, can affect the way the people view things. Reading has changed countless opinions and views of history and many other things around the world. Most people mature and develop better analytical skills from reading a wide variety of different literary pieces. â€Å"Hills Like White Elephants† by Ernest Hemingway, A Raisin in the Sun by Lorraine Hansberry, and â€Å"The Man He Killed† by Thomas Hardy are three pieces of literature that have significantly impacted me as a reader. â€Å"Hills Like White Elephants† by Hemingway is a short story about a girl who is put into a position to make an important decision. She sits with a man whom she has an intimate relationship with. While they sit at a train station, they discuss and argue about the important decision. The man portrays a masculine and controlling demeanor while the girl portrays dependence and a naà ¯ve type love towards the man. Throughout the story , the man tries to encourage the girl to make the decision, portraying a false sense of care for the girl. It is evident in the story that the man does not care for the girl as much as she cares for him. The man shows agitation towards the confused girl. While the girl questions her decision, the man already made his decision. The girl drinks throughout their argument to find courage. She continuously says that she is doing the operation for the man and not for herself. She just wants her relationship with the man to be back to theShow MoreRelatedâ€Å"the Lottery† and â€Å"Hills Like White Elephants† Essay881 Words   |  4 Pagesâ€Å"The Lottery† and â€Å"Hills like White Elephants† Regardless of the type of society people live in controversial topics and cowardly individuals can create conflict. 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Best Conclusion Of The Essay On Sikhism Example For Students

Best Conclusion Of The Essay On Sikhism God sends His messengers into the world from time to time to guidehumanity, states Professor Gobind Singh Mansukhani, author of the book,The Quintessence of Sikhism. Although Jesus Christ was considered to be sent toEarth between 8 BC and 4 BC by god, the ten Gurus, who found the Sikh religionfive hundred years ago in the Punjab region of India, were also considered to bemessengers of God (Jesus Christ 194-198; Mansukhani 1; Kleffman 1). These founders of the Sikh religion, unlike others of the time, recorded theirteachings and their beliefs in the Guru Granth Sahib, a holy book that isconsidered to be the eternal Guru (Sikh Missionary Center 244). The history,beliefs, and distinction from other religions make Sikhism a fascinatingreligion. Originating in the fifteenth century, Sikhism struggles to stay alivein India, even today. Guru Nanak Dev Ji, the founder of Sikhism established thisreligion, free from the discriminating ideas of Hinduism and Islam (Mansukhani2; Wolcott and Wolcott 48). Guru Nanak Dev Ji carried the Divine Light, whichallowed his body to be a platform for God to speak on. This light was passed onto the other nine Gurus who created the Guru Granth Sahib (Sikh MissionaryCenter 7-9). The eighth Guru, Guru Harkishan Dev Ji, became a Guru at the age offive (Guru Harkishan Dev Ji Internet). His knowledge and power awedpeople who realized he was really divine (Mansukhani 30-32). The lives of mostSikhs w ere threatened by religious hatred everyday. The fifth Guru, Guru ArjanDev Ji, and the ninth Guru, Guru Tegh Bahadur Ji, both became martyrs. GuruArjan Dev Ji was tortured with boiling water, thrown on burning sand, and wasseated on a red-hot plate because he would not give up his faith. Similarly,Guru Tegh Bahadur Ji also became a martyr. He refused to lose his faith and diedsaying Gods name. Today, Sikhs are still dying for their beliefs (Mansukhani23-25, 35-36). For Sikhs, their beliefs are declared in the Guru Granth Sahib. The Guru Granth Sahib contains the words of all ten Gurus and is the eternalGuru. This holy books teachings are protected in such a way that its followerswould notice if a comma or a period is out of place (Sikh Missionary Center 3,248). Sikhism opposes the caste system that existed in India. In fact, the Guruserased the caste system in Sikhs by creating a Langar system, which means GurusFree Kitchen. This system still exists today and requires everyone, rich orpoor, to sit side by side and share a meal, despite of social classes (Mansukhani15-16; Sikh Missionary Center 3-4). The Guru Granth Sahib also states womanshould be equal. Guru Nanak Dev Ji pointed out that women were never inferior tomen because they can get salvation also (Sikh Missionary Center 278). Besidespromoting equality, Sikhism respects other religions. The Guru Granth Sahibincludes excerpts from Hindu and Muslim saints, to show Sikhs to accept otherfaiths (Gurbani CD 6). All the beliefs of Sikhs are outlined in the holy bookwritten by the ten Gurus, themselves (Sikh Missionary Center 248). AlthoughSikhism is different from other religions, it is similar in many aspects also. Unlike other religions, everything people know about Sikhism comes from themouths of the Gurus. For example, The Sikh Missionary Center writesthere came Mahatma Buddh in India and he never wrote anything with hishands. After that came Christ who did not write anything himself. His teachingare only known through the Bible. Sikhism believes materialistic itemscome in the way of salvation (Sikh Missionary Center 3, 248, 249). Similarly,Buddhists also agree materialistic values get in the way of nirvana, the stateof peace (Buddhism 319-325). Sikhism, Hinduism, and Buddhism allsupport reincarnation (Sikh Missionary Center 253; Wolcott and Wolcott 36;Buddhism 322). Although there are several similarities with otherreligions, Sikhism is unique in its own way. Although times have changed, theSikh religion has remained unchanged for the last five hundred years (Kleffman1). The ten messengers God sent to Earth have helped form the Sikh religion (Mansukhani1). The holy book which the ten Gurus created is the living Guru, since it willlast forever and holds all the teachings of the past Gurus (Sikh MissionaryCenter 244). The ideas behind Sikhism make it a unique religion.