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Allen Rhodes
Allen Rhodes

Reputation: 56

Java: How to change values of instance variables with methods

I am completely new to Java and I much appreciate it if I could get a link to another thread that probably already covered this newb question.

But how do you change the value of an instance variable with a method? 

public class Example{
    private static int x = 1;
    private static String y;
    public static void setString(){
        if (x > 0){y = "Message A.";}
        else{y = "Message B.";}
    }
    public static void main(String args[]){
        System.out.print(y);         
    }
}

Upvotes: 2

Views: 20135

Answers (4)

Parul Rajput
Parul Rajput

Reputation: 11

To change the value of instance variable using method you need to use "setter" and "getter" method. Example :

public class ABC
  {
   private String name; // instance variable

   // method to set the name in the object       
  public void setName(String name)              
  {                                             
     this.name = name; // store the name        
  }                                             

  // method to retrieve the name from the object   
  public String getName()                          
  {                                                
     return name; 
  }                                                


   public static void main(String args[]){
    ABC b = new ABC();
   Scanner input = new Scanner(System.in);
   String name = input.nextLine(); // read a line of text
   b.setName(name); // put name in ABC  
   System.out.println("NAME IS "+ b.getName());

}

}

Upvotes: 1

Sathvik Hebbar
Sathvik Hebbar

Reputation: 1

To change the value of an instance variable, you need to use an instance method and such a method which changes the state of an instance is called a 'setter' or mutator. For example:

public class Example {
    private static int x = 1;

    private int a; // Instance variable
    private static String y;
    public static void setString(){
        if (x > 0){y = "Message A.";}
        else{y = "Message B.";}
    }
    public void setA(int a) { // This is a mutator
        this.a = a; // Sets the value of a to the specified 'a'
    }
    public void getA() { // This is an accessor
        return a; // we return a
    }

    public static void main(String args[]){
        Example k = new Example();
        k.setA(4);
        System.out.println(k.a);         
    }
}

Upvotes: 0

vbnr
vbnr

Reputation: 307

You need to access value of static variable using the class itself. Below code might gives you an idea. Function print is a non static function that is called by a instantiated object e.

      public class Example{
        private static int x = 1;
        private static String y;
        public static void setString(){
            if (x > 0){y = "Message A.";}
            else{y = "Message B.";}
        }
        public void print(){
            System.out.println("x "+x);
            System.out.println("y "+y);

        }
        public static void main(String args[]){
            System.out.print(y);
            Example.x = 0;
            Example e = new Example();
            Example.setString();
            e.print();

            }

    }

Upvotes: 0

Oleg Cherednik
Oleg Cherednik

Reputation: 18255

y is static variable, therefore it belongs to class (but not to class instance), therefore it is accessible from static method main. x == 1 => x > 0 therefore y = Message A.

public static void main(String args[]){
    setString();
    System.out.print(y);         
}

Upvotes: 2

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