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JAVA error: non-static method cannot be referenced from a static context

Posted on 2013-11-13
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Last Modified: 2013-11-14
I am new to JAVA and have the following code that is giving me the above error.  I don't know what is causing it.  Any help is greatly appreciated.

public class Chapter7Test
{
   public boolean XOR(boolean a, boolean b)
   {
      if((a && !b) || (!a && b))
      {
         return true;
      }
      if((a || b) && !(a && b))
      {
         return true;
      }
      if(( a != b))
      {
         return true;
      }
      return false;
   }
   
   public boolean DecimalRepresentation(int x)
   {
      if(x % 100 == 0 && x % 1000 != 0)
      {
         return true;
      }
      return false;
   }
   
   public boolean isLeapYear(int year)
   {
      return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
   } 
   
   public static void main(String [] args)
   {
   System.out.println(isLeapYear(2004));
   //boolean bResults=XOR(true,true);
   //System.out.print("test XOR a=true, b=true result=");
   //System.out.println(bResults);
   }
   

}

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This is the error I am getting when I compile:

Chapter7Test.java:36: error: non-static method isLeapYear(int) cannot be referenced from a static context
   System.out.println(isLeapYear(2004));
                      ^
1 error


Any help is greatly appreciated!
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Question by:dyarosh
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LVL 86

Expert Comment

by:CEHJ
ID: 39646418
You need to create an instance of Chapter7Test using the new operator before you can call its methods
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Author Comment

by:dyarosh
ID: 39646464
Forgive my ignorance but are you saying I need to put my methods in a different class?  Basically what I am trying to do is just test my methods which I thought I could do in the Main method.  If I don't need another class can you show me how to make the declaration in the main method?
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Accepted Solution

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CEHJ earned 2000 total points
ID: 39646525
Chapter7Test c7t = new Chapter7Test();
System.out.println(c7t.isLeapYear(2004));

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Expert Comment

by:jb1dev
ID: 39646837
Static methods are called on a class.
Instance methods (non-static methods) are called on an instance of a class.  

E.g.
public class A {
    public static void foo() { ... }
    public void baz() { ... }
}

public class EntryPoint {
    public static void main(String[] args) {
        A.foo(); // This works.
        A.baz(); // This does not work. Your compiler will complain about this.
        
        A a = new A();  // Now we have an instance of class "A" pointed to by a reference called "a". 
                                 // So now we can call instance methods on it.
        a.baz(); // This works.
    }
} 

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Author Closing Comment

by:dyarosh
ID: 39646851
Thanks a lot!
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LVL 86

Expert Comment

by:CEHJ
ID: 39647560
:)
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