Codes

public class Converter {

    private Double value;
    private String from;
    private String to;

    /**
     * @param value
     * @param metric
     */
    public Converter(Double value, String from, String to) {
        this.value = value;
        this.from = from;
        this.to = to;
    }

    /**
     * @return Double
     * @throws Exception must provide data.
     */
    public Double convert() throws Exception {
        switch (this.from) {
            case "in":
                switch (this.to) {
                    case "cm":
                        return this.value * 2.54;
                }
            default:
                throw new Exception("You didn't provide me with shit fucktard.");
        }
    }
}