An assignment for an advance java course at my local community college. The assignment asked for four separate files, as shown below. Periodic needed to be abstract and PeriodArray had contain both metals and nonmetals elements.

Periodic.java

/*
Kurt Kaiser
CTIM-168 E40
07.11.2018
*/

import java.util.Objects;

public abstract class Periodic
{
    // Instance Variables
    private String symbol;
    private int atomicNumber;
    private double atomicWeight;

    // Constructors
    public Periodic()
    {
        symbol = "none";
        atomicNumber = 0;
        atomicWeight = 0;
    }

    public Periodic(String newSymbol, int newAtomicNumber, double newAtomicWeight)
    {
        symbol = newSymbol;
        atomicNumber = newAtomicNumber;
        atomicWeight = newAtomicWeight;
    }

    // Getters
    public String getSymbol() {
        return symbol;
    }

    public int getAtomicNumber() {
        return atomicNumber;
    }

    public double getAtomicWeight() {
        return atomicWeight;
    }

    // Setters
    public void setAtomicNumber(int atomicNumber) {
        this.atomicNumber = atomicNumber;
    }

    public void setAtomicWeight(double atomicWeight) {
        this.atomicWeight = atomicWeight;
    }

    public void setSymbol(String symbol) {
        this.symbol = symbol;
    }

    public String toString() {
        return "Symbol:" + symbol +
                "\nAtomic Number: " + atomicNumber +
                "\nAtomicWeight: " + atomicWeight;
    }

    @Override
    public boolean equals(Object otherObject) {
        if (this == otherObject) return true;
        if (otherObject == null || getClass() != otherObject.getClass()) return false;
        Periodic periodic = (Periodic) otherObject;
        return atomicNumber == periodic.atomicNumber &&
                Double.compare(periodic.atomicWeight, atomicWeight) == 0 &&
                Objects.equals(symbol, periodic.symbol);
    }

    // Abstract method
    public abstract void describeElement();

}

PeriodicArray.java

/*
Kurt Kaiser
CTIM-168 E40
07.11.2018
*/

public class PeriodArray {

    public static void metals(PeriodicMetal[] metalsArray) {
        metalsArray[0] = new PeriodicMetal("Na", 11, 22.9897);
        metalsArray[1] = new PeriodicMetal("Ti", 22, 47.867);
        metalsArray[2] = new PeriodicMetal("Li", 3, 6.941);
    }

    public static void nonMetals(PeriodicNonMetal[] nonMetalsArray) {
        nonMetalsArray[0] = new PeriodicNonMetal("H", 1, 1.0079);
        nonMetalsArray[1] = new PeriodicNonMetal("He", 2, 4.0026);
        nonMetalsArray[2] = new PeriodicNonMetal("Se", 34, 78.96	);
    }

    public static void main(String[] args) {
        PeriodicMetal [] metalsArray = new PeriodicMetal[3];
        metals(metalsArray);
        int sum = 1;
        for (int i = 0; i < 3; i++){
            System.out.println("--- Metal " + sum + " ---\n" + metalsArray[i].toString());
            metalsArray[i].describeElement();
            sum++;
        }
        PeriodicNonMetal [] nonMetalsArray = new PeriodicNonMetal[3];
        nonMetals(nonMetalsArray);
        sum = 1;
        for (int c = 0; c < 3; c++){
            System.out.println("--- Non-Metal " + sum + " ---\n" + nonMetalsArray[c].toString());
            nonMetalsArray[c].describeElement();
            sum++;
        }
    }
}

PeriodicMetal.java

/*
Kurt Kaiser
CTIM-168 E40
07.11.2018
*/

public class PeriodicMetal extends Periodic
{
    public PeriodicMetal(){
        super();
    }

    public PeriodicMetal(String newSymbol, int newAtomicNumber, double newAtomicWeight){
        super(newSymbol, newAtomicNumber, newAtomicWeight);
    }

    public void describeElement(){
        System.out.println("Metals are good conductors.");
    }
}

PeriodicNonMetal.java

/*
Kurt Kaiser
CTIM-168 E40
07.11.2018
*/

public class PeriodicNonMetal extends Periodic
{
    public PeriodicNonMetal(){
        super();
    }

    public PeriodicNonMetal(String newSymbol, int newAtomicNumber, double newAtomicWeight){
        super(newSymbol, newAtomicNumber, newAtomicWeight);
    }

    public void describeElement(){
        System.out.println("Non-metals are not good conductors.");
    }
}