WrClasses-WE2-P1

Section 10.4 WrClasses-WE2-P1

Subgoals for Writing a Class.

Pick a name for the class, is usually a noun
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Differentiate class-level static vs. instance/object-level variables
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Differentiate class-level static vs. instance/object behaviors/methods
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Define instance variables (that you want to be interrelated)
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1. Name
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2. Data Type
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3. private
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Define class variables static as needed
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1. Name
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2. Data Type
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3. public / private / final
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Create constructor (behavior) that creates initial state of object
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1. Overloaded constructor (with as many parameters)
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2. public
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3. Same name as class
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4. No return type
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5. Default - no parameters
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6. Logic - initialize all variables
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7. Repeat as needed, adding parameters
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Create 1 accessor and 1 mutator behaviors per attribute
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1. Accessors
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  1. Name is get_<attr_name>
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  2. Public
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  3. Return type same data type as attribute
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  4. No parameters
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  5. Logic - return value
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2. Mutators
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  1. Name is set_<attr_name>
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  2. Public
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  3. Return type is void
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  4. Parameter is same data type as attribute
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  5. Logic validates input parameter and sets attribute value
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Write toString method
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1. public
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2. Returns String
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3. No parameters
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4. Logic - convert needed attributes to a format that can be printed
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Write equals method
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1. public
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2. Returns boolean
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3. Parameter - instance of the class
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4. Logic - compare attributes for equity
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Create additional methods as needed
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Subsection 10.4.1

Consider the SongType class you began in an earlier exercise, as illustrated in the following UML diagram.

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Exercises Exercises

1.

Q9: Put the code in the right order to complete the default constructor.

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public class SongType{
---
   //attributes declared here
   //...
   //default constructor
   public SongType(){
---
      title = "";
      artist = "";
      length = 0;
---
   }
}

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2.

Q10: Put the code in the right order to complete the specific overloaded constructor.

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public class SongType{
---
   //attributes declared here
   //...
   //overloaded constructor
   public SongType(String titleIn, String artistIn, double lengthIn){
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      title = titleIn;
      artist = artistIn;
      length = lengthIn;
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   }
}

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3.

Q11: Which of the following is NOT true about constructors?

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Constructors must be named the same name as the class
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Incorrect
Default constructors have no parameters
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Incorrect
Classes cannot have more than a single constructor
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Correct
Constructors must be public
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Incorrect
Constructors have no return type, not even void
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Incorrect

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4.

Q12: Two constructors are shown for the Point class below. Is this code valid?

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public class Point {
   private int x;
   private int y;

   public Point (int one, int two) {/*LOGIC*/}
   public Point (int a, int b) {/*LOGIC*/}
}

valid
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Incorrect
invalid
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Correct
cannot be determined
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Incorrect

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