{"id":104884,"date":"2020-05-19T10:00:35","date_gmt":"2020-05-19T07:00:35","guid":{"rendered":"https:\/\/www.javacodegeeks.com\/?p=104884"},"modified":"2020-05-18T16:09:26","modified_gmt":"2020-05-18T13:09:26","slug":"switch-as-an-expression-in-java-with-lambda-like-syntax","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2020\/05\/switch-as-an-expression-in-java-with-lambda-like-syntax.html","title":{"rendered":"Switch as an expression in Java with Lambda-like syntax"},"content":{"rendered":"

As of Java 14, the switch<\/code> expression has an additional Lambda-like<\/em> (case ... -> labels<\/code>) syntax and it can be used not only as a statement, but also as an expression that evaluates to a single value.<\/p>\n

Lambda-like<\/em> syntax (case ... -> labels<\/code>)<\/h2>\n

With the new Lambda-like<\/em> sytax, if a label is matched, then only the expression or statement to the right of the arrow is executed; there is no fall through:<\/p>\n

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var result = <\/code>switch<\/code> (str) {<\/code><\/div>\n
    <\/code>case<\/code> \"A\"<\/code> -> <\/code>1<\/code>;<\/code><\/div>\n
    <\/code>case<\/code> \"B\"<\/code> -> <\/code>2<\/code>;<\/code><\/div>\n
    <\/code>case<\/code> \"C\"<\/code> -> <\/code>3<\/code>;<\/code><\/div>\n
    <\/code>case<\/code> \"D\"<\/code> -> <\/code>4<\/code>;<\/code><\/div>\n
    <\/code>default<\/code> -> <\/code>throw<\/code> new<\/code> IllegalStateException(<\/code>\"Unexpected value: \"<\/code> + str);<\/code><\/div>\n
};<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

The above is an example of switch<\/code> as an expression returning an single integer value. The same syntax can be used in switch<\/code> as a statement:<\/p>\n

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int<\/code> result;<\/code><\/div>\n
switch<\/code> (str) {<\/code><\/div>\n
    <\/code>case<\/code> \"A\"<\/code> -> result = <\/code>1<\/code>;<\/code><\/div>\n
    <\/code>case<\/code> \"B\"<\/code> -> result = <\/code>2<\/code>;<\/code><\/div>\n
    <\/code>case<\/code> \"C\"<\/code> -> {<\/code><\/div>\n
        <\/code>result = <\/code>3<\/code>;<\/code><\/div>\n
        <\/code>System.out.println(<\/code>\"3!\"<\/code>);<\/code><\/div>\n
    <\/code>}<\/code><\/div>\n
    <\/code>default<\/code> -> {<\/code><\/div>\n
        <\/code>System.err.println(<\/code>\"Unexpected value: \"<\/code> + str);<\/code><\/div>\n
        <\/code>result = -<\/code>1<\/code>;<\/code><\/div>\n
    <\/code>}<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

yield<\/code><\/h2>\n

In the situation when a block is needed in a case<\/code>, yield<\/code> can be used to return a value from it:

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var result = <\/code>switch<\/code> (str) {<\/code><\/div>\n
    <\/code>case<\/code> \"A\"<\/code> -> <\/code>1<\/code>;<\/code><\/div>\n
    <\/code>case<\/code> \"B\"<\/code> -> <\/code>2<\/code>;<\/code><\/div>\n
    <\/code>case<\/code> \"C\"<\/code> -> {<\/code><\/div>\n
        <\/code>System.out.println(<\/code>\"3!\"<\/code>);<\/code><\/div>\n
        <\/code>yield <\/code>3<\/code>; <\/code>\/\/ return<\/code><\/div>\n
    <\/code>}<\/code><\/div>\n
    <\/code>default<\/code> -> <\/code>throw<\/code> new<\/code> IllegalStateException(<\/code>\"Unexpected value: \"<\/code> + str);<\/code><\/div>\n
};<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

Mutliple constants per case<\/code><\/h2>\n

It is also possible to use mutliple constants per case<\/code>, separated by comma, which futher simplifies the usage of switch<\/code>:<\/p>\n

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var result = <\/code>switch<\/code> (str) {<\/code><\/div>\n
    <\/code>case<\/code> \"A\"<\/code> -> <\/code>1<\/code>;<\/code><\/div>\n
    <\/code>case<\/code> \"B\"<\/code> -> <\/code>2<\/code>;<\/code><\/div>\n
    <\/code>case<\/code> \"C\"<\/code> -> <\/code>3<\/code>;<\/code><\/div>\n
    <\/code>case<\/code> \"D\"<\/code>, <\/code>\"E\"<\/code>, <\/code>\"F\"<\/code> -> <\/code>4<\/code>;<\/code><\/div>\n
    <\/code>default<\/code> -> <\/code>5<\/code>;<\/code><\/div>\n
};<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

Final example<\/h2>\n

To demonstrate new switch<\/code> syntax I created this tiny calculator:<\/p>\n

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double<\/code> calculate(String operator, <\/code>double<\/code> x, <\/code>double<\/code> y) {<\/code><\/div>\n
    <\/code>return<\/code> switch<\/code> (operator) {<\/code><\/div>\n
        <\/code>case<\/code> \"+\"<\/code> -> x + y;<\/code><\/div>\n
        <\/code>case<\/code> \"-\"<\/code> -> x - y;<\/code><\/div>\n
        <\/code>case<\/code> \"*\"<\/code> -> x * y;<\/code><\/div>\n
        <\/code>case<\/code> \"\/\"<\/code> -> {<\/code><\/div>\n
            <\/code>if<\/code> (y == <\/code>0<\/code>) {<\/code><\/div>\n
                <\/code>throw<\/code> new<\/code> IllegalArgumentException(<\/code>\"Can't divide by 0\"<\/code>);<\/code><\/div>\n
            <\/code>}<\/code><\/div>\n
            <\/code>yield x \/ y;<\/code><\/div>\n
        <\/code>}<\/code><\/div>\n
        <\/code>default<\/code> -> <\/code>throw<\/code> new<\/code> IllegalArgumentException(<\/code>\"Unknown operator '%s'\"<\/code>.formatted(operator));<\/code><\/div>\n
    <\/code>};<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

Source code<\/h2>\n

The source code for this article can be found on Github: https:\/\/github.com\/kolorobot\/java9-and-beyond<\/a><\/p>\n

References<\/h2>\n