How to correctly use HashMap?

Question

HashMap savedStuff = new HashMap();
savedStuff.put(\"symbol\", this.symbol); //this is a string
savedStuff.put(\"index\", this.index); //this is an int

Answer 1

Here is a different Approach:

A Helper class that contains a map and provides different views of it:

public class ValueStore {


    /**
     * Inner map to store values.
     */
    private final Map inner = new HashMap();

    /**
     * Returns true if the Value store contains a numeric value for this key.
     */
    public boolean containsIntValue(final String key){
        return this.inner.get(key) instanceof Integer;
    }


    /**
     * Returns true if the Value store contains a String value for this key.
     */
    public boolean containsStringValue(final String key){
        return this.inner.get(key) instanceof String;
    }

    /**
     * Returns the numeric value associated with this key.
     * @return -1 if no such value exists
     */
    public int getAsInt(final String key){
        final Object retrieved = this.inner.get(key);
        return retrieved instanceof Integer ? ((Integer) retrieved).intValue() : -1;
    }


    /**
     * Returns the String value associated with this key.
     * @return null if no such value exists
     */
    public String getAsString(final String key){
        final Object retrieved = this.inner.get(key);
        return retrieved instanceof String ? (String) retrieved : null;
    }

    /**
     * Store a string value.
     */
    public void putAsInt(final String key, final int value){
        this.inner.put(key, Integer.valueOf(value));
    }


    /**
     * Store an int value.
     */
    public void putAsString(final String key, final String value){
        this.inner.put(key, value);
    }

    /**
     * Main method for testing.
     */
    public static void main(final String[] args) {
        final ValueStore store = new ValueStore();
        final String intKey = "int1";
        final String stringKey = "string1";
        final int intValue = 123;
        final String stringValue = "str";

        store.putAsInt(intKey, intValue);
        store.putAsString(stringKey, stringValue);

        assertTrue(store.containsIntValue(intKey));
        assertTrue(store.containsStringValue(stringKey));
        assertFalse(store.containsIntValue(stringKey));
        assertFalse(store.containsStringValue(intKey));
        assertEquals(123, store.getAsInt(intKey));
        assertEquals(stringValue, store.getAsString(stringKey));
        assertNull(store.getAsString(intKey));
        assertEquals(-1, store.getAsInt(stringKey));
    }

}

Before you would retrieve an int value, you would check the value of store.containsIntValue(intKey) and before you retrieve a String value, you would check store.containsStringValue(stringKey). That way you would never retrieve values of the wrong type.

(Can of course be extended to support other types as well)