To avoid that, the best option is to declare the variable number as private and then use a setter to change it. A getter method on the other hand is the only possible way to read the value of the variable, outside the class:. For example:.
Java developers, whether they are beginners or have been coding for quite some time, often make mistakes in using Java getters and setters. To them, such mistakes may not seem too critical, but they cause errors in many different situations. Following are the most common mistakes made by Java developers when implementing getters and setters in Java.
The correct method is also mentioned along with each of them to know how such mistakes can be avoided. Here, the variable phoneNumber is declared as public, so it can be directly accessed using the dot. Any condition assigned in the setter will also be violated in case if the value is accessed using the dot operation.
The correct practice is to use a relatively more restricted access modifier like protected or more preferably, private:. Here, an array of integers, myData, is initialized with 5 values in line 1. The array is then passed to the setData method in line 2.
Now, in line 4, we have assigned a new value to the second element at the first index in the myData array:. You can see that that the value of the second element is now changed from 47 to 34 due to the assignment in line 4. You must have understood the point of it by now.
The data saved in the array can be modified from outside of the scope without using the setter method. This again makes the setter useless as well as breaks the encapsulation. But how does that happen? This means that both variables are referring to the myData array object in memory, so any changes made to either the data or myData variables are made on the same object.
A better practice for this situation is to copy elements from the newData array to the data array, one at a time. Now, the member variable data is not referring to the object which itself was referred to by the newData variable. Instead, the data is now initialized to a new array with the same size as the array newData.
Then, we copy all elements from the array newData to the data array, using System. Now, both invocations of displayData get the same output. It indicates that array data is independent and different from the array newData passed into the setter, thus the assignment statement will not affect the array data.
In the book Effective Java , Joshua Bloch points out this problem in item An array of integer numbers, myScores , is initialized with 6 values line 1 and the array is passed to the setScores method line 2. The method displayScores simply prints out all scores from the array:. These are all the elements of the myScores array.
Now, in line 4, we can modify the value of the 2 nd element in the myScores array as follows:. What will happen if we call the method displayScores again at line 5? Well, it will produce the following output:. You realize that the value of the 2 nd element is changed from 5 to 1, as a result of the assignment in line 4. Why does it matter? Well, that means the data can be modified outside the scope of the setter method, which breaks the encapsulation purpose of the setter.
And why does that happen? That means both of the variables are referring to the same object in memory — the myScores array object. So changes made to either the scores or myScores variables are actually made on the same object.
A workaround for this situation is to copy elements from the scr array to the scores array, one by one. The modified version of the setter would look like this:. Well, the member variable scores is no longer referring to the object referred by the scr variable. Instead, the array scores is initialized to a new one with size equals to the size of the array scr. Then, we copy all elements from the array scr to the array scores , using System.
Now, the two invocations of displayScores produce the same output. That means the array scores is independent and different than the array scr passed into the setter, thus we have the assignment:. Instead, you should find some ways to copy values of the passed object into the internal object, like we have copied elements from one array to another using the System.
As you notice, the 2 nd element of the array scores is modified outside the setter, in line 5. Because the getter method returns the reference of the internal variable scores directly, the outside code can obtain this reference and make a change to the internal object.
A workaround for this case is that, instead of returning the reference directly in the getter, we should return a copy of the object. This is so that the outside code can obtain only a copy, not the internal object. Therefore, we modify the above getter as follows:. So the rule of thumb is: Do not return a reference of the original object in the getter method. Instead, it should return a copy of the original object. So, mistakes 2 and 3 can easily be avoided.
For example, the following code is safe because the setter and getter are involved in a primitive type of float :. So, for primitive types, there is no special trick to correctly implement the getter and setter. String is an object type, but it is immutable, which means once a String object is created, its String literal cannot be changed. In other words, every change on that String object will result in a newly created String object.
So, like primitive types, you can safely implement getter and setter for a String variable, like this:. The java. Date class implements the clone method from the Object class. The method clone returns a copy of the object, so we can use it for the getter and setter, as shown in the following example:. The clone method returns an Object , so we must cast it to the Date type. You can learn more about this in item 39 of Effective Java by Joshua Bloch:.
According to the rules for implementing getter and setter, the three System. However, when running the above program, it produces the following output:. For a collection of Strings, one solution is to use the constructor that takes another collection as an argument. The reason for using getters and setters instead of making your members public is that it makes it possible to change the implementation without changing the interface. Also, many tools and toolkits that use reflection to examine objects only accept objects that have getters and setters.
JavaBeans for example must have getters and setters as well as some other requirements. You may also want to read " Why getter and setter methods are evil ":. In fact, they can damage your code's maintainability. Moreover, the presence of numerous getter and setter methods is a red flag that the program isn't necessarily well designed from an OO perspective.
I've used these A LOT because they are awesome. For example, make a setter that deals with an Number which displays that number on your webpage. When the setter is used it animates the old number to the new number using a tweener. If the initial number is 0 and you set it to 10 then you would see the numbers flip quickly from 0 to 10 over, let's say, half a second. Users love this stuff and it's fun to create. Here is an example to explain the most simple way of using getter and setter in java.
One can do this in a more straightforward way but getter and setter have something special that is when using private member of parent class in child class in inheritance. You can make it possible through using getter and setter. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How do getters and setters work?
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