For example, the "copy-paste reuse" anti-pattern is often applied by copying an old method and making some slight modifications to it, without proper refactoring. Sometimes, to make this work, one has to duplicate a member variable and modify that variable a little bit, too.
This might result in a class with too many instance variables more precise: too many very similar looking instance variables. In such a situation, the similar instance variables maybe an indicator for repeated code elsewhere in the class. However, as you noted, this is an artificial example, and I would not conclude a general rule from it. Too many instance variables means too much state. Too much state leads to duplicated code that is only slightly different for each of the states.
This is classic single concrete class doing too many things that should be sub-classes or compositions. Find a few classes that have too many instance variables, you will see they maintain way too much state and have lots of duplicated code paths that are only slightly specialized for each case, but so convoluted that they can not be broken apart into reusable methods.
This is one of the biggests sources of side effects as well. There is at least one exception to this that does not fall into this category and is an easy way to remediate this. Immutable objects do not have this problem, because they are a fixed state, there is not any chances for convoluted state management or side effects.
According to my experience, I cannot confirm that "many instance variables in general indicate duplicated code". Also, note that this belongs to the "code smells", and there are allegedly contradicting smells. Have a look here:. Amusingly, you will find "too many instance variables" is as good a code smell as "too few instance variables".
Every instance variable may mean some kind of status of the object. Stati always need a careful treatment. You must ensure that you have covered all possible combinations of stati in order to avoid unexpected behavior. You must always clearly now: which status does my object have right now?
From this angle, a lot of instance variables may indicated that the class has become unmaintainable. It may also indicate that a class does too many jobs, as it needs so many stati. Every instance variable requires you to keep oversight, which methods alter the variable in what way. So, suddenly, you don't know any longer all the cooks that are cooking.
One of them, programmed tiredly at late night, will spoil your soup. Again: too many of such variables will lead to code difficult to penetrate. The other side: too few instance variables may cause that many methods must handle their information with too much work and with too much parameters.
You feel this, if you are giving to many of your methods a certain equal parameter, and all methods do somehow a very similar thing with this parameter. In that situation, your code will start to bloat. You will end up scrolling many screens up and down in order to get some simple things together. Here, a refactoring may help: introduce one instance variable and one clear entrance to it. Instance variables can be accessed directly by calling the variable name inside the class.
However, within static methods when instance variables are given accessibility , they should be called using the fully qualified name. Online Demo. Rishi Raj. Previous Page Print Page. Sometimes you want to know if two reference variables refer to a single object on the heap.
But sometimes you want to know if two objects are equal. And for that, you need the. The idea of equality for objects depends on the type of object. But what about a Dog? Do you want to treat two Dogs as being equal if they happen to have the same size and weight? Probably not. So whether two different objects should be treated as equal depends on what makes sense for that particular object type. Use the equals method to see if two different objects are equal.
The rules are the same whether the variable is a reference or primitive. Roses are red, this poem is choppy, passing by value is passing by copy. Oh, like you can do better? Try it. Replace our dumb second line with your own. Put a checkmark next to the ones that are legal. Some statements are there to assign values used in the method calls. Each of the Java files on this page represents a complete source file. Your job is to play compiler and determine whether each of these files will compile.
Assume they always tell the truth about themselves. If they happen to say something that could be true for more than one guy, then write down all for whom that sentence applies.
Fill in the blanks next to the sentence with the names of one or more attendees. A short Java program is listed to your right. Two blocks of the program are missing. Not all the lines of output will be used, and some of the lines of output might be used more than once. Draw lines connecting the candidate blocks of code with their matching command-line output.
Your job is to take code snippets from the pool and place them into the blank lines in the code. Your goal is to make a class that will compile and run and produce the output listed. Note: Each snippet from the pool can be used only once! Fast Times in Stim-City. It should Nobody on the outside can access those methods buddy, nobody! When Jai heard Buchanan talk about his code, Buchanan never mentioned his instance variables.
Jai suspected that while Buchanan did in fact handle his methods correctly, he failed to mark his instance variables private. That slip up could have easily cost Leveler thousands. Skip to main content. Start your free trial. Chapter 4. Remember: a class describes what an object knows and what an object does. Can every object of that type have different method behavior?
The size affects the bark. You can send things to a method. You can get things back from a method. Note The bits representing 42 are returned from the giveSecret method, and land in the variable named theSecret. You can send more than one thing to a method. Calling a two-parameter method, and sending it two arguments. You can pass variables into a method, as long as the variable type matches the parameter type. Java is pass-by- value. That means pass-by- copy. There are no Dumb Questions Q: Q: What happens if the argument you want to pass is an object instead of a primitive?
Q: Q: Can a method declare multiple return values? A: A: Sort of. Q: Q: Do I have to return the exact type I declared? A: A: You can return anything that can be implicitly promoted to that type. Q: Q: Do I have to do something with the return value of a method?
Bullet Points Classes define what an object knows and what an object does. Things an object does are its methods behavior. Methods can use instance variables so that objects of the same type can behave differently.
A method can have parameters, which means you can pass one or more values in to the method. Cool things you can do with parameters and return types. Do it or risk humiliation and ridicule. Note By forcing everybody to call a setter method, we can protect the cat from unacceptable size changes. Hide the data. Note Mark instance variables private. Mark getters and setters public. HeadFirst: Can you give me an example? Encapsulating the GoodDog class.
0コメント