What is singleton class? Importance of Final in class? Can constructor have importing and exporting parameters? What is static construct and instance constructor? Difference between static and instance? When to use local class and when to use global class? How to create extra button on selection screen? Oops alv used? How to add logic for extra button created on alv screen? How to disable the radio button if another radio button is selected? How to make field editable using alv? How to colour a field using alv? What is bapi? What is IDOC? What is difference between association and navigation property in odata? How to check issue in odata if we are not getting values in frontend or getting some error? How nevagation properties are connected with frontend?