public Item newClassItem(final String value) {
        key2.set(7 /* CLASS */, value, null, null);
        Item result = get(key2);
        if (result == null) {
            pool.put12(7 /* CLASS */, newUTF8(value));
            result = new Item(index++, key2);
            put(result);
        }
        return result;
    }
Adds a number or string constant to the constant pool of the class being build. Does nothing if the constant pool
already contains a similar item.

@param cst the value of the constant to be added to the constant pool. This parameter must be an {@link Integer},
a {@link Float}, a {@link Long}, a {@link Double}, a {@link String} or a {@link Type}.
@return a new or already existing constant item with the given value.
src/main/java/com/alibaba/fastjson/asm/ClassWriter.java