Set and Get Methods in java

Question

How can I use the set and get methods  and why should I use them  Are they really helpful  And also can you give me examples of set and get methods

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this is the code for set method  public void setAge int age     this age   age

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It looks like you trying to do something similar to C  if you want setAge create method setAge int age   this age   age

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I want to add to other answers that setters can be used to prevent putting the object in an invalid state   For instance let s suppose that I ve to set a TaxId  modelled as a String  The first version of the setter can be as follows   private String taxId   public void setTaxId String taxId        this taxId   taxId      However we d better prevent the use to set the object with an invalid taxId  so we can introduce a check   private String taxId   public void setTaxId String taxId  throws IllegalArgumentException       if  isTaxIdValid taxId             throw new IllegalArgumentException  Tax Id      taxId      is invalid              this taxId   taxId      The next step  to improve the modularity of the program  is to make the TaxId itself as an Object  able to check itself   private final TaxId taxId   new TaxId    public void setTaxId String taxIdString  throws IllegalArgumentException       taxId set taxIdString     will throw exception if not valid     Similarly for the getter  what if we don t have a value yet  Maybe we want to have a different path  we could say   public String getTaxId   throws IllegalStateException       return taxId get      will throw exception if not set

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Setters and getters are used to replace directly accessing member variables from external classes   if you use a setter and getter in accessing a property  you can include initialization  error checking  complex transformations  etc   Some examples   private String x   public void setX String newX        if  newX    null            x             else           x   newX           public String getX         if  x    null            return           else          return x

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Having accessor methods is preferred to accessing fields directly  because it controls how fields are accessed  may impose data checking etc  and fits with interfaces  interfaces can not requires fields to be present  only methods

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public class Person   private int age   public int getAge         return age     public void setAge int age        this age   age        i think this is you want   and this also called pojo

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Set and Get methods are a pattern of data encapsulation  Instead of accessing class member variables directly  you define get methods to access these variables  and set methods to modify them  By encapsulating them in this manner  you have control over the public interface  should you need to change the inner workings of the class in the future   For example  for a member variable   Integer x    You might have methods   Integer getX    return x    void setX Integer x   this x   x        chiccodoro also mentioned an important point  If you only want to allow read access to the field for any foreign classes  you can do that by only providing a public get method and keeping the set private or not providing a set at all

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I think you want something like this   public class Person      private int age       public method to get the age variable   public int getAge           return this age          public method to set the age variable   public void setAge int age          this age   age          You re simply calling such a method on an object instance  Such methods are useful especially if setting something is supposed to have side effects  E g  if you want to react to certain events like     public void setAge int age           this age   age          double averageCigarettesPerYear   this smokedCigarettes   1 0   age          if averageCigarettesPerYear  gt   7300 0               this eventBus fire new PersonSmokesTooMuchEvent this                   Of course this can be dangerous if somebody forgets to call setAge int  where he should and sets age directly using this age

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just because the OOP rule  Data Hiding and Encapsulation  It is a very bad practice to declare a object s as public and change it on the fly in most situations   Also there are many other reasons   but the root is Encapsulation in OOP   and  buy a book or go read on Object Oriented Programming    you will understand everything on this after you read any book on OOP

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This answer is merged from another question   Your getAge   method is called instance method in Java    To invoke an instance method  you should have a object of the Class in which this method is defined   For Example  If this method in a Class called Person  then   Create a Person object using new operator   Person p   new Person     To get the age of a Person object  use this method  p getAge

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The above answers summarize the role of getters and setters better than I could  however I did want to add that your code should ideally be structured to reduce the use of pure getters and setters  i e  those without complex constructions  validation  and so forth  as they break encapsulation  This doesn t mean you can t ever use them  stivlo s answer shows an example of a good use of getters and setters   just try to minimize how often you use them   The problem is that getters and setters can act as a workaround for direct access of private data  Private data is called private because it s not meant to be shared with other objects  it s meant as a representation of the object s state  Allowing other objects to access an object s private fields defeats the entire purpose of setting it private in the first place  Moreover  you introduce coupling for every getter or setter you write  Consider this  for example   private String foo   public void setFoo String bar        this foo   bar      What happens if  somewhere down the road  you decide you don t need foo anymore  or you want to make it an integer  Every object that uses the setFoo method now needs to be changed along with foo

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The benefits of get   set   methods are as follows      You can serialize you object easily  You can create a persistent object from the containing class  You can convert the properties to JSON easily  In the DAO layer  Frameworks like Hibernate  you can directly save the object to DB  Easy understanding of object oriented concept  Needs in all design pattern except possibly in single tone pattern  Security for properties protecting direct access  Polymorphism  Encapsulation can be easily understood and implemented by this type of class    Example   private String personName  private int personId       public void setPersonName String name  throws Exception      if   name equals      name              this personName   name              public String getPersonName        return this personName        public void setPersonId int id  throws Exception      this personId   id        public int getPersonId        return this personId

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I don t see a simple answer to the second question  why  here  So here goes   Let s say you have a public field that gets used very often in your code  Whenever you decide you need to do something extra before you give or set this field you have a problem  You have to create a special getter and setter for this field and change your complete code from using the field directly to using the getter and setters    Now imagine you are developing a library widely used by many people  When you need to make a change like the above and set direct access of the field to private the code of all the people using this field will break   Using getters and setters is about future planning of the code  it makes it more flexible  Of course you can use public fields  especially for simple classes that just hold some data  But it s always a good idea to just make the field privately and code a get and set method for it

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Above answers all assume that the object in question is an object with behaviour  An advanced strategy in OOP is to separate data objects  that do zip  only have fields  and behaviour objects    With data objects  it is perfectly fine to omit getters and instead have public fields  They usually don t have setters  since they most commonly are immutable - their fields are set via the constructors  and never again  Have a look at Bob Martin s Clean Code or Pryce and Freeman s Growing OO Software    for details

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Some benefits of using getters and setters  known as encapsulation or data-hiding     originally answered here      1  The fields of a class can be made read-only  by only providing the getter  or write-only  by only providing the setter   This gives the class a total control of who gets to access modify its fields    Example   class EncapsulationExample       private int readOnly   -1      this value can only be read  not altered     private int writeOnly   0        this value can only be changed  not viewed     public int getReadOnly             return readOnly            public int setWriteOnly int w            writeOnly   w               2  The users of a class do not need to know how the class actually stores the data  This means data is separated and exists independently from the users thus allowing the code to be more easily modified and maintained  This allows the maintainers to make frequent changes like bug fixes  design and performance enhancements  all while not impacting users       Furthermore  encapsulated resources are uniformly accessible to each user and have identical behavior independent of the user since this behavior is internally defined in the class    Example  getting a value    class EncapsulationExample       private int value      public int getValue                  return value     return the value           Now what if I wanted to return twice the value instead  I can just alter my getter and all the code that is using my example doesn t need to change and will get twice the value   class EncapsulationExample       private int value      public int getValue             return value 2     return twice the value              3  Makes the code cleaner  more readable and easier to comprehend    Here is an example   No encapsulation   class Box       int widthS     width of the side     int widthT     width of the top        other stuff           Box b   new Box    int w1   b widthS      Hm    what is widthS again   int w2   b widthT      Don t mistake the names  I should make sure I use the proper variable here    With encapsulation   class Box       private int widthS     width of the side     private int widthT     width of the top     public int getSideWidth             return widthS            public int getTopWIdth             return widthT               other stuff           Box b   new Box    int w1   b getSideWidth       Ok  this one gives me the width of the side int w2   b getTopWidth       and this one gives me the width of the top  No confusion  whew    Look how much more control you have on which information you are getting and how much clearer this is in the second example  Mind you  this example is trivial and in real-life the classes you would be dealing with a lot of resources being accessed by many different components  Thus  encapsulating the resources makes it clearer which ones we are accessing and in what way  getting or setting    Here is good SO thread on this topic   Here is good read on data encapsulation

[java] Set and Get Methods in java?

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