Lecture 12 Objectives [Nov 13]prev next

MUSICAL COMPOSITION: Tchaikovsky Piano Concerto No.1 (premiered in Boston, Massachusetts on 25 Oct 1875)
 

Movement I (part 1) 12:16	Movement I (part2 ) 12:09	Movement II 8:41	Movement III 8:31

At the end of today's class you should

HAVE READ:

• [251-268][271-272]
• Code examples for Nov-13 via Eclipse/SourceForge, showing how to properly invoke static methods

KNOW:

• The concept of a static variable
• The concept of a static method
• The difference between an instance variable and a static variable
• The difference between an instance method and a static method
• How to define a class constant (public static final <type> <constName> = <value>) [p. 47-48]

BE ABLE TO:

• Create a common static Scanner object to be used by a Program, rather than being forced to pass it back and forth via parameters

DAILY QUESTION:

• You are given a String value that contains a sequence of characters representing a number (i.e., such as "1238.17". What statement(s) should you execute to set a float variable to be equal to this actual value? Would you statements have been any different if the string had been of the form "2003"?
  
   

  String s = "1238.17"; float f; // some statements that you must provide. // when this executes, the goal is to output 1238.17 to the screen System.out.println (f);

Sample Exam Question:

1. A class has an instance method inst(), a static method stat(), and an instance variable data of type int.
• Inside the body of inst, it is impossible to have the statement "inst();" (TRUE / FALSE)
• Inside the body of stat, it is impossible to have the statement "data = 20;" (TRUE / FALSE)
• Inside the body of stat, it is impossible to have the statement "inst();" (TRUE / FALSE)
2. Given the Student class, which we have been using for our examples in lecture (as shown below), you have been asked to add a method that determines whether a particular student is a high school student (year of grad = 'HS') or a graduate student (year of grad = 'GS'). Write the method and be sure to include (a) documentation; (b) method signature; (c) method implementation. Be sure to clarify whether this is a static method or a non-static method.
   
    

   public class Student {   /** Unique id. */   String id;   /** Student Name. */   String name;   /** Year of graduation. */   String yearOfGrad;   /** Major. */   String major; }

    

3. Given the Student class above, you have been asked to add a method that returns true if a given String represents an actual year of graduation (i.e., only contains digits '0' through '9') or returns false if the given String contains non-digit characters. Write the method and be sure to include (a) documentation; (b) method signature; (c) method implementation. Be sure to clarify whether this is a static method or a non-static method.
    
4. Assume that you change the class definition for Student as below (just showing instance variables and static variables):
   
    

   public class Student {   /** Unique id. */   String id;   /** Student Name. */   String name;   /** Year of graduation. */   static String yearOfGrad;   /** Major. */   String major;   ... }

   Assume you have a program that uses the Student class and it processes a set of students. Under what circumstances will the output of the program be unaffected by this change?
    

5. Assume you have a class that contains a static variable count and an instance method meth(). If it is legal for meth() to update count provide one reason why this might be useful; if it is not legal for meth() to update count, explain the reason why it is illegal.