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Constructors, Instance Variables, and Parameters

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Constructors, Instance Variables, and Parameters, Double and Char won't compile properly

xosunkist	20 Apr, 2007 - 01:33 PM Post #1
D.I.C Head Joined: 28 Mar, 2007 Posts: 69 My Contributions	Coding project file should have two classes. The program class is named StudentStart and the object class is named Student. The Student class should be used to create three student objects. Each student object should be instantiated with five arguments using a constructor to initialize the instance variables. The instance variables should contain the student's name, their student number and the scores they received on each of three tests worth 100 points if they received all the possible points. The average grade for the three test scores should be calculated and a letter grade determined for the average grade in the constructor when the student object is instantiated. The Student class should also contain the writeOutput method used to display on the monitor the student name, student number, test scores receive, average grade for the three test scores and the letter grade the student will receive. (Here is what I have below for this project. It does not compile or recognize the double or char. What am I doing wrong?) CODE /* The Student class contains four constructors that are used to initialize variables when Student objects are created. It also contains the output method used by the program StudentStart.java to output information about the object to the monitor Constructors are used to initialize variables. A constructor does not use a return type in the heading. Also a constructor's name is identical to the class name. Constructors cannot be invoked except when a new object is created. / public class Student { / String, double, and char variables declared but not initialized./ private String stName; private String stStudentid; private double Testone; private double Testtwo; private double Testthree; private char Letter; / This constructor is called the default constructor because it has no parameters and receives no arguments. / public Student() { stName = "Student Name: "; stStudentid = "Student #: "; Testone = "TESTING: "; Testtwo = "TESTING: "; Testthree = "TESTING: "; Letter = "TESTING: "; } / end of Student default constructor -/ / This constructor is used when new objects are created with one String argument. / / The first line of the method is called the method heading. The statements between the { } curly braces are considered the body of the method. Together they are called the method definition. The writeOutput method return type void because it returns no values to the computer. It is public so any program can access it. This method is used in this program to print the current values of the instance variables in each object when the respective object calls the writeOutput method./ public Student(String stName, String stStudentid, double Testone, double Testtwo, double Testthree) { stName = "Student Name: " + stName + ""; stStudentid = "Student #: " + stStudentid + ""; Testone = "Grades: " + Testone + Testtwo + Testthree + ""; Letter = "Letter Grade: " + Letter + "\n\n"; } public void writeOutput() { System.out.println(stName); System.out.println(stStudentid); System.out.println(Testone); System.out.println(Testtwo); System.out.println(Testthree); System.out.println(Letter); } / end of writeOutput method / } /end of class Student/ and StudentStart CODE / This is a simple program to demonstrate how java can create three student objects from a class called Student using four constructors in the Student class. A Student constructor is called for each of the objects you create. However a different constructor is called for each object since a different number of arguments is sent to the constructor each time. The constructor is used if the constructors parameters match the arguments sent in type and number. The three objects we create are named StudentA, StudentB and StudentC. We are using two class files in this project. They are Student in the StudentStart.java file and Student in the Student.java file. StudentStart is the program file because it contains the method named: public static void main(String[] args) / public class StudentStart { public static void main(String[] args) { / Each of the following statements creates a Student object by making a copy of the class named Student. It then assigns them different names. These objects are named StudentA, StudentB and StudentC. We refer to this as instantiating (making an instant copy of the class) We initialize variables in these objects using constructors. The arguments in the parentheses are used by the constructor to initialize the instance variables in the object in accordance with the method definition for the constructor. In this example the new objects are enclosed in quotation marks as literal strings because the constructors use type String parameters./ Student studentA = new Student("Ugly Betty", "789", "100", "80", "90", "C"); Student studentB = new Student("Mary Jane", "123", "80", "75", "65", "B"); Student studentC = new Student("Luke Sky", "456", "70", "65", "86", "A"); / The following statements call the output method in each of the objects as indicated. The name to the left of the period is the object name and the name to the right of the period is the output method. Remember you cannot call any of the constructor methods after the object has been created. The output method illustrates displays information showing a different constructor was used to initialize the variables in each object./ studentA.writeOutput(); studentB.writeOutput(); studentC.writeOutput(); } /end of main method/ } /end of class StudentStart*/
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beef	RE: Constructors, Instance Variables, And Parameters 20 Apr, 2007 - 02:01 PM Post #2
D.I.C Head Joined: 2 Nov, 2006 Posts: 128 My Contributions	For one, you are trying to put strings in your double variables. That won't work. CODE //Bad Testone = "TESTING"; //Better (the little d tells java this is a double instead of an int) Testone = 0d; Another problem I see is in your constructor where you pass in values, you aren't specifying which Testone you are putting stuff in, and java will put it in the one that is most local. You should either use different names for your input variables or add a this. in front of your first set of values like this: CODE this.Testone = Testone; This post has been edited by beef: 20 Apr, 2007 - 02:02 PM
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xosunkist	RE: Constructors, Instance Variables, And Parameters 20 Apr, 2007 - 02:39 PM Post #3
D.I.C Head Joined: 28 Mar, 2007 Posts: 69 My Contributions	I guess I don't understand. What about the char? QUOTE(beef @ 20 Apr, 2007 - 03:01 PM) For one, you are trying to put strings in your double variables. That won't work. CODE //Bad Testone = "TESTING"; //Better (the little d tells java this is a double instead of an int) Testone = 0d; Another problem I see is in your constructor where you pass in values, you aren't specifying which Testone you are putting stuff in, and java will put it in the one that is most local. You should either use different names for your input variables or add a this. in front of your first set of values like this: CODE this.Testone = Testone;
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xosunkist	RE: Constructors, Instance Variables, And Parameters 20 Apr, 2007 - 02:48 PM Post #4
D.I.C Head Joined: 28 Mar, 2007 Posts: 69 My Contributions	Okay, now I need the other two grades to show up and they aren't. I'm supposed to have three grades and then average them with a letter grade. Revised Student.java CODE /* The Student class contains four constructors that are used to initialize variables when Student objects are created. It also contains the output method used by the program StudentStart.java to output information about the object to the monitor Constructors are used to initialize variables. A constructor does not use a return type in the heading. Also a constructor's name is identical to the class name. Constructors cannot be invoked except when a new object is created. / public class Student { / String, double, and char variables declared but not initialized./ private String stName; private String stStudentid; private double Grades; private char Letter; / This constructor is called the default constructor because it has no parameters and receives no arguments. / public Student() { stName = "Student Name: "; stStudentid = "Student #: "; Grades = 0d; Letter = Letter; } / end of Student default constructor -/ / This constructor is used when new objects are created with one String argument. / / The first line of the method is called the method heading. The statements between the { } curly braces are considered the body of the method. Together they are called the method definition. The writeOutput method return type void because it returns no values to the computer. It is public so any program can access it. This method is used in this program to print the current values of the instance variables in each object when the respective object calls the writeOutput method./ public Student(String stName, String stStudentid, double Grades) { stName = "Student Name: " + stName + ""; stStudentid = "Student #: " + stStudentid + ""; Grades = "Grades: " + Grades + ""; Letter = "Letter Grade: " + Letter + ""; } public void writeOutput() { System.out.println(stName); System.out.println(stStudentid); System.out.println(Grades); System.out.println(Letter); } / end of writeOutput method / } /end of class Student/ Revised StudentStart.java CODE / This is a simple program to demonstrate how java can create three student objects from a class called Student using four constructors in the Student class. A Student constructor is called for each of the objects you create. However a different constructor is called for each object since a different number of arguments is sent to the constructor each time. The constructor is used if the constructors parameters match the arguments sent in type and number. The three objects we create are named StudentA, StudentB and StudentC. We are using two class files in this project. They are Student in the StudentStart.java file and Student in the Student.java file. StudentStart is the program file because it contains the method named: public static void main(String[] args) / public class StudentStart { public static void main(String[] args) { / Each of the following statements creates a Student object by making a copy of the class named Student. It then assigns them different names. These objects are named StudentA, StudentB and StudentC. We refer to this as instantiating (making an instant copy of the class) We initialize variables in these objects using constructors. The arguments in the parentheses are used by the constructor to initialize the instance variables in the object in accordance with the method definition for the constructor. In this example the new objects are enclosed in quotation marks as literal strings because the constructors use type String parameters./ Student studentA = new Student("Ugly Betty", "789", "100", "80", "90", "C"); Student studentB = new Student("Mary Jane", "123", "80", "75", "65", "B"); Student studentC = new Student("Luke Sky", "456", "70", "65", "86", "A"); / The following statements call the output method in each of the objects as indicated. The name to the left of the period is the object name and the name to the right of the period is the output method. Remember you cannot call any of the constructor methods after the object has been created. The output method illustrates displays information showing a different constructor was used to initialize the variables in each object./ studentA.writeOutput(); studentB.writeOutput(); studentC.writeOutput(); } /end of main method/ } /end of class StudentStart*/
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beef	RE: Constructors, Instance Variables, And Parameters 20 Apr, 2007 - 03:17 PM Post #5
D.I.C Head Joined: 2 Nov, 2006 Posts: 128 My Contributions	For the char it's kind of the same, a char can only hold one letter and it's not exactly the same as a string. If you want to give it a value use single quotes instead of double ex. CODE char Letter = 'a'; The way you have it now, Student is only accepting name, id and grades(as one value) If you need to display all three, you'll have to keep track of all three in Student. An easy way to do this would be an array if you've covered that yet. If not, use 3 values like you had before.
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xosunkist	RE: Constructors, Instance Variables, And Parameters 20 Apr, 2007 - 03:19 PM Post #6
D.I.C Head Joined: 28 Mar, 2007 Posts: 69 My Contributions	Here is a code I worked on previously that compiled with no errors. When I submitted it to my teacher this is what he said: You will need to use String and numbers. So, you have: private String stNumber; private String stMake; private String stTestone; private String stTesttwo; private String stTestthree; private String stLetter; First, of all make doesn't make sense here. That was for a Car, a car has a make, model. Well, you're dealing with a Student here so these should be something like: name, studentId finally, like I said we don't want to use all String types. The Test scores should be of type int or type double. The stLetter should be of type char as it is a single character. So, when you create a student you don't need all those constructors you copied from the Car example, you really only need 1. That constructor will take 5 parameters. The first 2 will be String (for name and id) and the last 3 will be numbers for each of the test scores. then, inside the body of the constructor you can compute the average (you still need to create an instance variable for that) After you compoute the average, you can use an if statment (still inside the constructor) to determin what letter grad the student will receive. STUDENT.JAVA : CODE /* The Student class contains four constructors that are used to initialize variables when Student objects are created. It also contains the output method used by the program StudentStart.java to output information about the object to the monitor Constructors are used to initialize variables. A constructor does not use a return type in the heading. Also a constructor's name is identical to the class name. Constructors cannot be invoked except when a new object is created. / public class Student { / String variables declared but not initialized./ private String stNumber; private String stMake; private String stTestone; private String stTesttwo; private String stTestthree; private String stLetter; / This constructor is called the default constructor because it has no parameters and receives no arguments. / public Student() { stNumber = "Student Name: "; stMake = "Student #: "; stTestone = "Grade 1: "; stTesttwo = "Grade 2: "; stTestthree = "Grade 3: \n\n"; } / end of Student default constructor -/ / This constructor is used when new objects are created with one String argument. / public Student(String objectNum) { stNumber = "Student Name: " + objectNum + ""; stMake = "Student #: "; stTestone = "Grade 1: "; stTesttwo = "Grade 2: "; stTestthree = "Grade 3: \n\n"; } / end of Student constructor -- one parameter / / This constructor is used when new objects are created with two String arguments. / public Student(String objectNum, String make) { stNumber = "Student Name: " + objectNum + ""; stMake = "Student #: " + make + ""; stTestone = "Grade 1: "; stTesttwo = "Grade 2: "; stTestthree = "Grade 3: \n\n"; } / end of Student constructor -- two parameters / / This constructor is used when new objects are created with three String arguments. / public Student(String objectNum, String make, String Testone) { stNumber = "Student Name: " + objectNum + ""; stMake = "Student #: " + make + ""; stTestone = "Grade 1: " + Testone + " \n\n"; stTesttwo = "Grade 2: "; stTestthree = "Grade 3: \n\n"; } / end of Student constructor -- three parameters / public Student(String objectNum, String make, String Testone, String Testtwo) { stNumber = "Student Name: " + objectNum + ""; stMake = "Student #: " + make + ""; stTestone = "Grade 1: " + Testone + ""; stTesttwo = "Grade 2: " + Testtwo + ""; stTestthree = "Grade 3: "; stLetter = "Letter Grade: \n\n"; } / The first line of the method is called the method heading. The statements between the { } curly braces are considered the body of the method. Together they are called the method definition. The writeOutput method return type void because it returns no values to the computer. It is public so any program can access it. This method is used in this program to print the current values of the instance variables in each object when the respective object calls the writeOutput method./ public Student(String objectNum, String make, String Testone, String Testtwo, String Testthree) { stNumber = "Student Name: " + objectNum + ""; stMake = "Student #: " + make + ""; stTestone = "Grade 1: " + Testone + ""; stTesttwo = "Grade 2: " + Testtwo + ""; stTestthree = "Grade 3: " + Testthree + ""; stLetter = "Letter Grade: \n\n"; } public Student(String objectNum, String make, String Testone, String Testtwo, String Testthree, String letter) { stNumber = "Student Name: " + objectNum + ""; stMake = "Student #: " + make + ""; stTestone = "Grade 1: " + Testone + ""; stTesttwo = "Grade 2: " + Testtwo + ""; stTestthree = "Grade 3: " + Testthree + ""; stLetter = "Letter Grade: " + letter + "\n\n"; } public void writeOutput() { System.out.println(stNumber); System.out.println(stMake); System.out.println(stTestone); System.out.println(stTesttwo); System.out.println(stTestthree); System.out.println(stLetter); } / end of writeOutput method / } /end of class Student/ STUDENTSTART.JAVA : CODE / This is a simple program to demonstrate how java can create three student objects from a class called Student using four constructors in the Student class. A Student constructor is called for each of the objects you create. However a different constructor is called for each object since a different number of arguments is sent to the constructor each time. The constructor is used if the constructors parameters match the arguments sent in type and number. The three objects we create are named StudentA, StudentB and StudentC. We are using two class files in this project. They are Student in the StudentStart.java file and Student in the Student.java file. StudentStart is the program file because it contains the method named: public static void main(String[] args) / public class StudentStart { public static void main(String[] args) { / Each of the following statements creates a Student object by making a copy of the class named Student. It then assigns them different names. These objects are named StudentA, StudentB and StudentC. We refer to this as instantiating (making an instant copy of the class) We initialize variables in these objects using constructors. The arguments in the parentheses are used by the constructor to initialize the instance variables in the object in accordance with the method definition for the constructor. In this example the new objects are enclosed in quotation marks as literal strings because the constructors use type String parameters./ Student studentA = new Student("Ugly Betty", "789", "100", "80", "90", "C"); Student studentB = new Student("Mary Jane", "123", "80", "75", "65", "B"); Student studentC = new Student("Luke Sky", "456", "70", "65", "86", "A"); / The following statements call the output method in each of the objects as indicated. The name to the left of the period is the object name and the name to the right of the period is the output method. Remember you cannot call any of the constructor methods after the object has been created. The output method illustrates displays information showing a different constructor was used to initialize the variables in each object./ studentA.writeOutput(); studentB.writeOutput(); studentC.writeOutput(); } /end of main method/ } /end of class StudentStart*/
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beef	RE: Constructors, Instance Variables, And Parameters 20 Apr, 2007 - 03:52 PM Post #7
D.I.C Head Joined: 2 Nov, 2006 Posts: 128 My Contributions	You're right, it would be better to use doubles for the score and a char for letter, but if you're teacher wants you to do it this way, do it so you get the grade and learn the right way on the side if you have to. This post has been edited by beef: 20 Apr, 2007 - 03:52 PM
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xosunkist	RE: Constructors, Instance Variables, And Parameters 20 Apr, 2007 - 03:53 PM Post #8
D.I.C Head Joined: 28 Mar, 2007 Posts: 69 My Contributions	Hello, I just have some questions to my project. I have attached a new revised version. A lot of compiler issues. Still haven't gotten to do the averages yet, still stuck on this part. Here is what I have been working on below: --------------------------------------------------------------> I have changed Testone, Testtwo, and Testthree to type double. I have changed letter to type char. See below: public Student(String Name, String Id, double Testone, double Testtwo, double Testthree, char letter) ------------------------------------------------------------------------------------------------------------------- I also changed this as well from String to double and char: private String stName; <----- Stays a String private String stId; <----- Stays a String private double stTestone; <------ changed to double private double stTesttwo; <----- changed to double private double stTestthree; <------ changed to double private char stLetter; <-------- changed to char ---------------------------------------------------------------------------------------------------------------- I think apart of my problem lies in here somewhere, but I changed the last item. stName = "Student Name: "; stId = "Student #: "; stTestone = "Grade 1: "; stTesttwo = "Grade 2: "; stTestthree = "Grade 3: \n\n"; char stletter = 'a'; <--------------------changed --------------------------------------------------------------------------------------------------------------------- I corrected my constructor so it includes five parameters as shown below: public Student(String Name, String Id, double Testone, double Testtwo, double Testthree) { stName = "Student Name: " + Name+ ""; stId= "Student #: " + Id + ""; stTestone = "Grade 1: " + Testone + ""; stTesttwo = "Grade 2: " + Testtwo + ""; stTestthree = "Grade 3: " + Testthree + ""; stLetter = "Letter Grade: " + letter + "\n\n"; } public void writeOutput() { System.out.println(stName); System.out.println(stId); System.out.println(stTestone); System.out.println(stTesttwo); System.out.println(stTestthree); System.out.println(stLetter); } ------------------------------------------------------------------------------------------------------------------------ On the StudentStart.java I get this error message below: --------------> C:\cs151\StudentStart.java:16: cannot find symbol symbol : constructor Student(java.lang.String,java.lang.String,java.lang.String,java.lang.String,java.lang.String,java.lang.String) location: class Student Student studentA = new Student("Ugly Betty", "789", "100", "80", "90", "C"); ^ C:\cs151\StudentStart.java:20: cannot find symbol symbol : constructor Student(java.lang.String,java.lang.String,java.lang.String,java.lang.String,java.lang.String,java.lang.String) location: class Student Student studentB = new Student("Mary Jane", "123", "80", "75", "65", "B"); ^ C:\cs151\StudentStart.java:24: cannot find symbol symbol : constructor Student(java.lang.String,java.lang.String,java.lang.String,java.lang.String,java.lang.String,java.lang.String) location: class Student Student studentC = new Student("Luke Sky", "456", "70", "65", "86", "A"); ^ .\Student.java:35: incompatible types found : java.lang.String required: double stTestone = "Grade 1: "; ^ .\Student.java:37: incompatible types found : java.lang.String required: double stTesttwo = "Grade 2: "; ^ .\Student.java:39: incompatible types found : java.lang.String required: double stTestthree = "Grade 3: \n\n"; ^ .\Student.java:56: incompatible types found : java.lang.String required: double stTestone = "Grade 1: " + Testone + ""; ^ .\Student.java:58: incompatible types found : java.lang.String required: double stTesttwo = "Grade 2: " + Testtwo + ""; ^ .\Student.java:60: incompatible types found : java.lang.String required: double stTestthree = "Grade 3: " + Testthree + ""; ^ .\Student.java:62: incompatible types found : java.lang.String required: char stLetter = "Letter Grade: " + letter + "\n\n"; ^ 10 errors Tool completed with exit code 1 --------------------------------------------------------------------------------------------------------------------------------- On the Student.java, I get this error message: ----------------> C:\cs151\Student.java:35: incompatible types found : java.lang.String required: double stTestone = "Grade 1: "; ^ C:\cs151\Student.java:37: incompatible types found : java.lang.String required: double stTesttwo = "Grade 2: "; ^ C:\cs151\Student.java:39: incompatible types found : java.lang.String required: double stTestthree = "Grade 3: \n\n"; ^ C:\cs151\Student.java:56: incompatible types found : java.lang.String required: double stTestone = "Grade 1: " + Testone + ""; ^ C:\cs151\Student.java:58: incompatible types found : java.lang.String required: double stTesttwo = "Grade 2: " + Testtwo + ""; ^ C:\cs151\Student.java:60: incompatible types found : java.lang.String required: double stTestthree = "Grade 3: " + Testthree + ""; ^ C:\cs151\Student.java:62: incompatible types found : java.lang.String required: char stLetter = "Letter Grade: " + letter + "\n\n"; ^ 7 errors Tool completed with exit code 1 -------------------------------------------------- NEW CODE !! NEW CODE !!! BELOW: STUDENT.JAVA ------------------------------------------------- CODE public class Student { private String stName; private String stId; private double stTestone; private double stTesttwo; private double stTestthree; private char stLetter; public Student() { stName = "Student Name: "; stId = "Student #: "; stTestone = "Grade 1: "; stTesttwo = "Grade 2: "; stTestthree = "Grade 3: \n\n"; char stletter = 'a'; } public Student(String Name, String Id, double Testone, double Testtwo, double Testthree, char letter) { stName = "Student Name: " + Name + ""; stId = "Student #: " + Id + ""; stTestone = "Grade 1: " + Testone + ""; stTesttwo = "Grade 2: " + Testtwo + ""; stTestthree = "Grade 3: " + Testthree + ""; stLetter = "Letter Grade: " + letter + "\n\n"; } public void writeOutput() { System.out.println(stName); System.out.println(stId); System.out.println(stTestone); System.out.println(stTesttwo); System.out.println(stTestthree); System.out.println(stLetter); } } --------------------------------------------- NEW CODE!! NEW CODE!! BELOW: STUDENTSTART.JAVA ---------------------------- CODE public class StudentStart { public static void main(String[] args) { Student studentA = new Student("Ugly Betty", "789", "100", "80", "90", "C"); Student studentB = new Student("Mary Jane", "123", "80", "75", "65", "B"); Student studentC = new Student("Luke Sky", "456", "70", "65", "86", "A"); studentA.writeOutput(); studentB.writeOutput(); studentC.writeOutput(); } }
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Amadeus	RE: Constructors, Instance Variables, And Parameters 20 Apr, 2007 - 03:58 PM Post #9
g++ -o drink whiskey.cpp Joined: 12 Jul, 2002 Posts: 12,348 Thanked: 51 times Dream Kudos: 25 My Contributions	The first errors are coming because you are passing all you parameters to the constructor as strings, when in reality only the first two and last should be. Remove the quotes from the numbers in the call to the constructors, and perhaps use single quotes for the final parameter. The other errors occur because the parameters are incorrect.
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