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${empty myMap}
${myMap[entry]}
${3+counter}

Tip: empty is an operator used to test whether a map, a collection, an array or a string is null or empty.

Tip: myMap[entry] is a way to access an element of a map. In other words, it is the same as myMap.get(entry) in Java.

When an EL expression is used as an attribute value, it could return any kind of objects as long as the component accepts it. For example, the following expression will be evaluated to a Boolean object.

<window if="${some > 10}">

Standard implicit objects, such as param and requestScope, and ZK implicit objects, such as self and page, are supported to simplify the use.

<textbox value="${param.who} does ${param.what}"/>




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