macOS Beginner Java Problem...

[noel4r]

Hello all, I just learning java and I'm having a hell of a time figuring objects and classes, constructors, static and non-static, etc. Anyway, I have a simple problem that I can't figure out. The output from the program below
is:
Name0 null Units 0 Grade A
Grade Points 4
Name0 null Units 0 Grade B
Grade Points 3
Name0 null Units 0 Grade C
Grade Points 2

Question is, why are the Names null and the Units 0, but the Grade and Grade Points displays the correct info?

import java.util.*;
public class temp
{
	public static void main (String[] arg)
	{

	Student[] studentList = new Student[3];

	studentList[0] = new Student("Name0");
	studentList[1] = new Student("Name1");
	studentList[2] = new Student("Name2");
	studentList[0] = new Student(4);
	studentList[1] = new Student(4);
	studentList[2] = new Student(3);
	studentList[0] = new Student('A');
	studentList[1] = new Student('B');
	studentList[2] = new Student('C');
	
	for (Student e : studentList)
	{
		System.out.println("Name0 " + e.getName() + " Units " + e.getUnits() + " Grade " + e.getGrade());
		System.out.println("Grade points " + e.getGradePoints());
	}			
	}// main

}

class Student

{

	//constructor
	public Student (String n)

	{
		name = n;
	}
	
	public Student(int u)
	{
		units = u;
	}
	
	public Student(char g)
	{
		grade = g;
	}

	//methods
	public String getName()
	{
		return name;
	}
	
	public int getUnits()
	{
		return units;
	}
	
	public char getGrade()
	{
		return grade;
	}
	public int getGradePoints()
	{
		value = 0;
		
		if (grade == 'A')
			value = 4;
		else if (grade == 'B')
			value = 3;
		else if (grade == 'C')
			value = 2;
		else if (grade == 'D')
			value = 1;			
		else if (grade == 'F')
			value = 0;
		return value;

	}
	
	String name;
	int units;
	char grade;
	int value;
}

 

[bbarnhart]

Your constructor needs to have three parameters, Name, Units and Grade

public Students (String n, int u, char g)
{
  name = n;
  unit = u;
  grade = g;
}

Create a new student like this

studentList[0] = new Student ("Brian", 10, 'A');
studentList[1] = new Student ("noel4r", 8, 'B');
studentList[2] = new Student ("Bush", 0, 'F');

What you are doing now is creating 9 Student objects when you only need to create three.

 

[960design]

Check out GreenFoot.org

It will quickly and visually teach you the concepts of object oriented design. You'll build a simple wombat 'game' in the process.

I'm in the process of creating a local high school programming app club that will teach the fundamentals of app development, good code design and it all pretty much begins with GreenFoot