Trying to replace a switch statement with an enum in Java

Question

I have the following class, which is using a switch statement and I'd like to replace it with an enum.

public class FillTable {

    private static final int NAME_INDEX = 0;
    private static final int DESCRIPTION_INDEX = 1;
    private static final int CONTRIBUTION_INDEX = 2;

    public Object getValueAt(int row, int col) {
        EmployeeData employeeData = (EmployeeData)items.get(row);

        switch (col) {
            case NAME_INDEX: {
                return employeeData.getName();
            }
            case DESCRIPTION_INDEX: {
                return employeeData.getDescription();
            }
            case ADDRESS_INDEX: {
                return employeeData.getAddress();
            }
            default: {
                return "";
            }
        }
    }

}

Here is the enum that I've come up with.

public enum EmployeeTableColumn {

    NAME_INDEX {
        @Override
        public void getData() {
            employeeData.getName();
        }
    }, DESCRIPTION_INDEX {
        @Override
        public void getData() {
            return employeeData.getDescription();
        }
    }, CONTRIBUTION_INDEX {
        @Override
        public void getData() {
            return employeeData.getAddress();
        }
    };

    public abstract void getData();

}

My problem is that I don't know how to replace the code in the getValueAt() method to make use of the enum in place of the switch statement. Can someone please show me how I can do this?

Give this answer a look: stackoverflow.com/questions/6391777/switch-on-enum-in-java Also, here is a nice example from the Java docs: docs.oracle.com/javase/tutorial/java/javaOO/enum.html — Nathan
– Nathan, Commented Jan 30, 2019 at 15:37

khelwood · Accepted Answer · 2019-01-30 20:54:11Z

2

If you want the EmployeeTableColumn enum to control how you extract information from an EmployeeData object, then you need a method in EmployeeTableColumn that takes your EmployeeData as a parameter and returns the extracted information.

public enum EmployeeTableColumn {
    NAME {
        @Override
        public Object getData(EmployeeData data) {
            return data.getName();
        }
    },
    DESCRIPTION {
        @Override
        public Object getData(EmployeeData data) {
            return data.getDescription();
        }
    },
    CONTRIBUTION {
        @Override
        public Object getData(EmployeeData data) {
            return data.getAddress();
        }
    };

    public abstract Object getData(EmployeeData data);
}

Then you can write a method that uses an EmployeeTableColumn to extract the correct data.

public Object getValueAt(int row, int col) {
    EmployeeData employeeData = (EmployeeData)items.get(row);

    // however you are going to pick the right column object
    EmployeeTableColumn employeeColumn = EmployeeTableColumn.values()[col];

    return employeeColumn.getData(employeeData);
}

edited Jan 30, 2019 at 20:54

answered Jan 30, 2019 at 15:42

khelwood

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4 Comments

Steve B Over a year ago

That worked, thanks! However, I don't understand how col can be mapped to either NAME_INDEX, DESCRIPTION_INDEX or CONTRIBUTION_INDEX? For example, there's no NAME_INDEX = 0

Mark Over a year ago

@SteveB EmployeeTableColumn.values() returns an array, ararys start with index 0, since NAME_INDEX is the first value in the enum this is located in .values()[0], and DESCRIPTION_INDEX is located in .values()[1] etc..

Steve B Over a year ago

@Mark, how would it work if for example the enum values weren't 0, 1 and 2? For example if NAME_INDEX was 246 and DESCRIPTION_INDEX was 877

Mark Over a year ago

@SteveB You can take a look at Can I set enum start value in Java?, that'll answer your question

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