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VALUES THAT ERROR IN SWITCH CASE JAVA HOW TO
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VALUES THAT ERROR IN SWITCH CASE JAVA SERIES

If There is not matched then it will return the default statement. In the Switch statement, using passing value and then this value will go down the list of the case to find matched one.

The expression must also have its value available at compile time. DecemA Java switch statement is matched case (condition) and execute statement for that.

The matched expression must be “simple.” It can’t contain any type checks, if statements, or extractors.

The matched value must be a known integer.

In his book, Scala In Depth (Manning), Joshua Suereth states that the following conditions must be true for Scala to apply the tableswitch optimization: When you look at that output, you’ll see that the tableswitch shown in the previous example is now gone. You can confirm this by running the javap command on the SwitchDemo.class file that was generated. This warning message is saying that neither a tableswitch nor lookupswitch could be generated for the match expression. SwitchDemo.scala:7: warning: could not emit switch for annotated match

VALUES THAT ERROR IN SWITCH CASE JAVA CODE

Version 2 - leads to a compiler warningĪgain, compile the code with scalac, but right away you’ll see a warning message: Next, make a minor change to the code, replacing the integer literal 2 with a value: This shows that Scala was able to optimize your match expression to a tableswitch. The output from this command shows a tableswitch, like this: Next, disassemble that file with this javap command: First, place the following code in a file named SwitchDemo.scala:Ĭompiling this class produces no warnings and creates the output file SwitchDemo.class. The effect of the annotation is demonstrated with a simple example.

VALUES THAT ERROR IN SWITCH CASE JAVA SERIES

If present, the compiler will verify that the match has been compiled to a tableswitch or lookupswitch, and issue an error if it instead compiles into a series of conditional expressions.” “An annotation to be applied to a match expression. Here’s the official description from the annotation documentation: When a value is given to the expression, it can jump directly to the result rather than working through the decision tree. This annotation provides a warning at compile time if the switch can’t be compiled to a tableswitch or lookupswitch.Ĭompiling your match expression to a tableswitch or lookupswitch is better for performance, because it results in a branch table rather than a decision tree. When writing simple match expressions like this, it’s recommended to use the annotation. A more functional approach returns a value from a match expression:Ĭase _ => "Invalid month" // the default, catch-all

VALUES THAT ERROR IN SWITCH CASE JAVA HOW TO

That example shows how to take an action based on a match. catch the default with a variable so you can print itĬase whoa => println("Unexpected case: " + whoa.toString) To use a Scala match expression like a Java switch statement, use this approach: You have a situation in your Scala code where you want to create something like a simple Java integer-based switch statement, such as matching the days in a week, months in a year, and other situations where an integer maps to a result. This is Recipe 3.7, “How to use a Scala match expression like a switch statement.” Problem This is an excerpt from the 1st Edition of the Scala Cookbook (partially modified for the internet). show more info on classes/objects in repl.