how to describe a recursion in an non static method. Now the recursion is not working

Question

I want to go through a binary tree recursive in the method public void inorder(). Afterwards I want to give out all the values which are in the binary tree. But in my case the recursive process does not work.Can somebody help?

I tried to do the recursive process with a static method but of course it is not working. I do not know how can I write the recursive process different from a static method recursive method. That is may problem. Can somebody help?

class BinaryNode {
    private BinaryNode leftSon, rightSon;
    private int value;

    public BinaryNode(int v) {
        value = v;
    }

    public boolean contains(int v) { 
        if ( ( leftSon != null) & ( rightSon != null) )
        if ( v == value ) return true;
        else
            if ( v < value ) leftSon.contains( v ) ;
            else rightSon.contains( v );
        return false;
    }

    public void insert(int v) { 
        if ( v != value ) {
            if ( v < value ) {
                BinaryNode links = new BinaryNode( v );
            }  
        } else {
            BinaryNode rechts = new BinaryNode( v );
        }  
    }

    public void inorder() { 
        if ( leftSon != null ) { inorder( ) ; }
        System.out.println( value );
        if ( rightSon != null ) { inorder( ) ; }
        System.out.println( value );
    }
}