import dev.cerus.easyitem.EasyItem;
import dev.cerus.easyitem.tokenizer.Token;
import dev.cerus.easyitem.tokenizer.Tokenizer;
import dev.cerus.easyitem.exception.ParserException;
import dev.cerus.easyitem.parser.Parser;
import dev.cerus.easyitem.parser.ParserBuilder;
import java.util.List;

class MyClass {

    public ItemStack makeStackQuick(String str) {
        // You could also use EasyItem#parse(String) but that 
        // would require you to catch a ParserException
        return EasyItem.unsafeParse(str);
    }

    public ItemStack makeStack(String str) {
        try {
            List<Token<?>> tokens = new Tokenizer(str)
                    .tokenize();
            Parser parser = new ParserBuilder(tokens)
                    .defaultTransformers()
                    .transformers(/*Add additional transformers here*/)
                    .build();
            // EasyItem#newDefaultParser(List<Token<?>>) also 
            // returns this exact parser
            return parser.parse();
        } catch (ParserException ex) {
            ex.printStackTrace();
            System.err.println("Invalid item string");
            return null;
        }
    }

}

import dev.cerus.easyitem.tokenizer.Token;
import dev.cerus.easyitem.exception.ParserException;
import dev.cerus.easyitem.parser.Parser;
import dev.cerus.easyitem.parser.Transformer;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;

class MyTransformer implements Transformer {

    @Override
    public void transform(ItemStack itemStack, Parser parser) throws ParserException {
        // Consume the two words "with" and "isodd"
        parser.consume();
        parser.consume();

        // Consume next token which should be our number
        Token<?> numToken = parser.consume();
        if (numToken.getType() != Token.Type.INTEGER
                && numToken.getType() != Token.Type.LONG) {
            throw new ParserException("Not a (valid) number");
        }

        // Get number and make odd/even bool
        long num = numToken.getValueUnsafe();
        boolean odd = (num & 1) == 1;

        ItemMeta meta = itemStack.getItemMeta();
        meta.setDisplayName(odd ? "Is odd" : "Is even");
        itemStack.setItemMeta(meta);
    }

    @Override
    public boolean matches(Parser parser) {
        // It's important to check if we do have tokens available before we peek
        return parser.has() // Is parser index < tokens?
                && parser.peek().equals(Token.Type.WORD, "with")
                && parser.has(1) // Is parser index + 1 < tokens?
                && parser.peekNext().equals(Token.Type.WORD, "isodd");
    }
}