public Put addItemEntry(String key, AttributeValue value) {
        if (null == this.item) {
            this.item = new java.util.HashMap<String, AttributeValue>();
        }
        if (this.item.containsKey(key))
            throw new IllegalArgumentException("Duplicated keys (" + key.toString() + ") are provided.");
        this.item.put(key, value);
        return this;
    }
Add a single Item entry

@see Put#withItem
@returns a reference to this object so that method calls can be chained together.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/model/Put.java