Create a ConfigurationObject class.

build.gradle

@@ -14,6 +14,7 @@ repositories {
 }
 
 dependencies {
+    compile 'com.moandjiezana.toml:toml4j:0.7.1'
     testCompile 'junit:junit:4.12'
 }
 

src/org/nwapw/abacus/config/Configuration.java

@@ -0,0 +1,18 @@
+package org.nwapw.abacus.config;
+
+/**
+ * Serializable class that will be used to load TOML
+ * configurations.
+ */
+public class Configuration {
+
+    /**
+     * The precision to which the calculator should operator.
+     */
+    public int decimalPrecision;
+    /**
+     * The type of number this calculator should use.
+     */
+    public String numberType;
+
+}

src/org/nwapw/abacus/config/ConfigurationObject.java

@@ -0,0 +1,146 @@
+package org.nwapw.abacus.config;
+
+import com.moandjiezana.toml.Toml;
+import com.moandjiezana.toml.TomlWriter;
+import org.nwapw.abacus.number.NaiveNumber;
+
+import java.io.File;
+import java.io.IOException;
+import java.lang.reflect.InvocationTargetException;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A configuration object, which essentially
+ * manages saving, loading, and getting values
+ * from the configuration. While Configuration is
+ * the data model, this is the interface with it.
+ */
+public class ConfigurationObject {
+
+    /**
+     * The default implementation to use for instantiating numbers.
+     */
+    private static final Class<? extends NaiveNumber> DEFAULT_IMPLEMENTATION = NaiveNumber.class;
+    /**
+     * The writer used to store the configuration.
+     */
+    private static final TomlWriter TOML_WRITER = new TomlWriter();
+    /**
+     * The configuration instance being modeled.
+     */
+    private Configuration configuration;
+    /**
+     * A map of number names to their implementations, which
+     * will be provided by plugins.
+     */
+    private Map<String, Class<? extends NaiveNumber>> numberImplementations;
+
+    /**
+     * Sets up the ConfigurationObject.
+     * different constructors do different things,
+     * but they all lead here.
+     * @param configuration the configuration to set up with.
+     */
+    private void setup(Configuration configuration){
+        this.configuration = configuration;
+        numberImplementations = new HashMap<>();
+    }
+
+    /**
+     * Creates a default configuration.
+     * @return the newly created default configuration.
+     */
+    private Configuration getDefaultConfig(){
+        configuration = new Configuration();
+        configuration.decimalPrecision = -1;
+        configuration.numberType = "naive";
+        return configuration;
+    }
+
+    /**
+     * Register a number implementation.
+     * @param name the name of the number implementation to register the class as.
+     * @param newClass the class that will be used to instantiate the new number.
+     *                 It is required that this class provides a Number(String) constructor.
+     */
+    public void registerImplementation(String name, Class<? extends NaiveNumber> newClass){
+        numberImplementations.put(name, newClass);
+    }
+
+    /**
+     * Creates a new number with the configured type, passing
+     * it the given string.
+     * @param string the string from which the number should be parsed.
+     * @return the resulting number, or null if an error occurred.
+     */
+    public NaiveNumber numberFromString(String string)  {
+        Class<? extends NaiveNumber> toLoad =
+                numberImplementations.getOrDefault(configuration.numberType, DEFAULT_IMPLEMENTATION);
+        try {
+            return toLoad.getConstructor(String.class).newInstance(string);
+        } catch (InstantiationException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
+            e.printStackTrace();
+        }
+        return null;
+    }
+
+    /**
+     * Returns the configured, user-requested precision.
+     * @return the precision.
+     */
+    public int getPrecision(){
+        return configuration.decimalPrecision;
+    }
+
+    /**
+     * Saves the ConfigurationObject to the given file.
+     * @param toFile the file to save ot.
+     * @return true if the save succeed, false if otherwise.
+     */
+    public boolean save(File toFile){
+        if(toFile.getParentFile() != null) toFile.getParentFile().mkdirs();
+        try {
+            TOML_WRITER.write(configuration, toFile);
+            return true;
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return false;
+    }
+
+    /**
+     * Creates a new configuration object with the given config.
+     * @param config the config to use.
+     */
+    public ConfigurationObject(Configuration config){
+        setup(config);
+    }
+
+    /**
+     * Create a configuration object by attempting to
+     * load a config from the given path, using the
+     * default configuration otherwise.
+     * @param path the path to attempt to load.
+     */
+    public ConfigurationObject(File path){
+        Configuration config;
+        if(!path.exists()) {
+            config = getDefaultConfig();
+        } else {
+            Toml parse = new Toml();
+            parse.read(path);
+            config = parse.to(Configuration.class);
+        }
+        setup(config);
+    }
+
+    /**
+     * Creates a new configuration object with the
+     * default configuration.
+     */
+    public ConfigurationObject(){
+        setup(getDefaultConfig());
+    }
+
+}