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Thread: have code - need one line fixed please!

  1. #1
    Junior Member
    Join Date
    Jul 2012
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    Default have code - need one line fixed please!

    hihi! here's my prompt and i think i did the program right but I can't get it to work

    how do i fix this program?

    this is the prompt btw: Create a S tudent class that stores the name, address, GPA, age, and major for a student. Additionally, the
    S tudent class should implement the C omparable interface. Make the comparison of S tudent objects
    based on the name, then the address, then the major, and finally the GPA. If the difference between two
    objects when compared lies in the name, return a 1 or -1 depending on which object is lessor/greater.
    If the difference in objects is in the address, return +/- 2. If the difference is in the major, return +/- 3. If the
    difference is in the GPA, return +/- 4. Only return zero if all 4 fields are the same. This behavior deviates
    slightly from the normal c ompareTo behavior (<0, 0, or >0), but we are ok with that for the purposes of
    this lab.
    Write a class called S tudentDriver to test your new method. Hard code several students into the main
    method of the S tudentDriver class with small differences in different fields. That is, make one student
    have one name and another a second name. Make a third student have the same name as the first, but a have
    the third student have a different address, etc. Make sure your c ompareTo method finds each the
    differences correctly.

    the first is my comparable and the second is my driver

    public class Student implements Comparable {
    String name;
    String address;
    String major;
    double gpa;
    public int compareTo(Object st) {
    	Student s = (Student) st;
    	if(this.name.compareTo(s.name) == 0) {
    		if(this.address.compareTo(s.address) == 0) {
    			if(this.major.compareTo(s.major) ==0) {
    				if(this.gpa == s.gpa) {
    					return 0; }
    				else if(this.gpa < s.gpa) {
    					return -4; }
    				else {
    					return 4; }}
    			else {
    				return 3 * this.major.compareTo(s.major); }}
    		else {
    			return 2 * this.address.compareTo(s.address); }}
    	else {
    		return this.name.compareTo(s.name);}

    public class StudentDriver{
        public static void main(String[] args) {
          Student st = new Student();
          Student Bob = new Student("Bob", "3 Bella Vista Court", "Phys", .8);
          Student Bob = new Student("Bob", "4 Bella Vista Court", "Chem", .9);
          Student Bob = new Student("Janice", "8 Bella Vista Court", "Eng", .7);
          Student Bob = new Student("Ian", "5 Bella Vista Court", "Math", .2);            
    Last edited by ash12; August 7th, 2012 at 08:20 PM.

  2. #2
    Join Date
    Jul 2012
    Thanked 2 Times in 2 Posts

    Default Re: have code - need one line fixed please!

    Student implements an interface with name Comparable.So it has to implement,thus write body of every single function of the interface.If one or more functions of the interface is left without an implementation,then the class that implements the interface has to be abstract.What i am saying in code is like this
    package airplane;
    public interface AirplaneInterface {
        void print(String runway);
        void setEngines(boolean on);
        void setGears(boolean down);
    and i have another file
    package airplane;
    public class AirplaneSuperclass implements AirplaneInterface {
        private boolean[] enginesIdle;
        private short enginesNumber;
        private int altitude;
        private String state;//taxiing,landing etc.
        private String flightNo;
        private boolean gearDown;
        private String type;
        void print(String runway)
        void setEngines(boolean on)
         void setGears(boolean down)
    everything ok.
    Now if function setEngines was not implemented(had a body) then i would get the error
     java.lang.RuntimeException: Uncompilable source code - airplane.AirplaneSuperclass is not abstract and does not override abstract method setEngines (boolean on) in airplane.AirplaneInterface
    	at airplane.AirplaneSuperclass.<clinit>(AirplaneSuperclass.java:4)

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