2 hours ago, Pegasus said:

great example,

but if you input item name with Apostrophe character, e.g Greenman's ale,

it doesn't print anything.

Updated my answer to fix this issue.

Items are known constants, so make an enumerator and populate it with relevant items. Enumerators can also have interfaces implemented into them, so you can include an item filter and then simply refer to the entries:

public enum ItemData implements Filter<Item> {

	ABYSSAL_WHIP(4151, "Abyssal whip"),
	COINS(995, "Coins"),
	;

	private final int id;
	private final String name;

	private ItemData(int id, String name) {
		this.id = id;
		this.name = name;
	}

	@Override
	public String toString() {
		return String.format("[%s] %s", id, name);
	}

	@Override
	public boolean match(Item item) {
		return item.getId() == id || item.getName().equals(name);
	}

	public int getId() {
		return id;
	}

	public String getName() {
		return name;
	}
}

Then you can do:

Item item1 = inventory.getItem(ItemData.ABYSSAL_WHIP);

Item item2 = inventory.getItem(ItemData.values());