Select when in java

Java When Method: Java-Method Explained

Java is a popular programming language used for developing applications for a variety of platforms, from mobile devices to embedded systems. One of its most powerful components is the when method, which provides an easy way to handle exceptions and quickly break out of code when needed. But what does the when method do, and when should it be used? This article will explain the when method and give advice on best practices for its usage.

What is Java When Method?

The when method is a built-in Java language tool which allows the developer to execute a set of instructions inside a block, and then break out of that block if an exception occurs. The full syntax of the when method is given below:

The condition can be an expression, such as a comparison, or a more detailed set of conditions such as an if statement. The instructions to execute will be whatever code the developer wishes to execute in case of an exception.

The when method is a powerful tool for handling exceptions in Java. It allows the developer to quickly and easily handle any exceptions that may occur in their code, without having to write a lot of extra code. This makes it a great tool for writing robust and reliable code.

How Does the Java When Method Work?

When an exception occurs, the when method is triggered and the code breaks out of the block, skipping all of the other instructions that were supposed to follow. This provides an easy way for developers to address exceptions without having to use try-catch blocks or other forms of error handling. It also prevents the user from having to anticipate exceptions before they occur.

For example, if the condition for the when statement is a comparison and the comparison returns false, then the code block will execute normally, but if the comparison returns true then the code block will be skipped and execution jumps to the next section of code.

The when method is a powerful tool for developers, as it allows them to quickly and easily handle exceptions without having to write complex error handling code. Additionally, it can be used to create more efficient code, as it eliminates the need to check for exceptions before they occur. This can help to reduce the amount of time and resources needed to develop an application.

Benefits of the Java When Method

The most obvious benefit of using the when method is that it provides an easy way to write code that handles exceptions. This gives the flexibility to choose how errors are handled, without having to rely on try-catch blocks or other error handling systems. It also allows developers to write concise code that targets exceptions without having to anticipate them.

In addition, using the when method can improve performance by avoiding excess code execution. This is especially beneficial for large projects where skipping unnecessary code execution can save time and resources.

The when method also allows for more efficient debugging, as it allows developers to quickly identify the source of an exception and take the necessary steps to resolve it. This can help reduce the amount of time spent debugging and improve the overall development process.

Potential Drawbacks of the Java When Method

While the when method provides a number of advantages, it also has some drawbacks. The most significant of these is that it can make code more difficult to debug, since it increases the number of possible execution paths. This can make it harder for developers to spot errors and create test cases.

In addition, the when method can lead to unexpected side effects when not used properly; for example, if the condition returns true unexpectedly then it can cause the code to skip over important instructions or logic. Therefore, it’s important to take care when using the when method and make sure that the conditions are well-defined and unlikely to return false unexpectedly.

Furthermore, the when method can also lead to code that is difficult to maintain and update. This is because the conditions used in the when statement can become outdated or irrelevant over time, making it difficult to keep the code up to date. Additionally, the when method can also lead to code that is difficult to read and understand, as the conditions used in the when statement can be complex and hard to follow.

Examples of the Java When Method in Practice

The following code is an example of how the when method can be used to check for an exception and break out of a code block:

This example shows how the when statement can be used to check for exceptions without having to use try-catch blocks. If the condition evaluates to true, then the code inside the block is executed and execution jumps to the end of the block. If not, then nothing happens and execution continues inside the try statement.

The when method is a powerful tool for handling exceptions in Java. It allows developers to quickly and easily check for exceptions and handle them without having to write complex try-catch blocks. This makes code more readable and easier to maintain.

Best Practices for Using the Java When Method

When using the when method, it’s important to ensure that conditions are well-defined and unlikely to return false unexpectedly. This is especially important for complex conditions or comparisons with large inputs. It’s also important to ensure that any exceptions are handled appropriately with meaningful messages for users.

In addition, it’s recommended to keep code concise and avoid overusing the when statement. Using it too often can make code difficult to debug and maintain, and can cause unexpected side effects.

When using the when method, it’s also important to consider the performance implications of the code. If the when statement is used in a loop, it can cause a significant performance hit. It’s best to use the when statement only when necessary, and to use other methods such as if-else statements when possible.

Alternatives to the Java When Method

For developers who don’t wish to use the when method, there are a few alternatives that provide similar functionality. For example, try-catch blocks can be used to handle exceptions in a similar way but with more control over how errors are handled. In addition, developers could use a library such as Apache Commons Utils which provides additional error handling mechanisms.

In conclusion, the Java when method provides an easy way to handle exceptions without having to use more complex alternative solutions such as try-catch blocks or libraries. However, it’s important for developers to ensure that conditions are well-defined and unlikely to return false unexpectedly, and that any exceptions are handled appropriately.

It is also important to consider the performance implications of using the when method. Depending on the complexity of the conditions being evaluated, the when method may be slower than using try-catch blocks or other alternatives. Therefore, it is important to consider the performance implications when deciding which approach to use.

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Switch to when

By Eugene Petrenko March 15, 2017 Comment Tweet Like

‘when’ expression in Kotlin VS ‘switch’ statement in Java

Switch in Java

Consider the following code in Java

void action(Bar bar)  Foo f; switch(bar)  case Bar.VALUE: f = value42(); case Bar.ELSE: f = value444(); default: throw ThisCanNeverHappenException(); > doSomeMightyWork(f); >

Widespread pattern, isn’t it? There are several things wrong with it! First, Foo f variable is not final, so it can be ocassionally changed in the future after some code changes.

Next, we switll have default branch which is not necessary as we cover all enum values. But if someone dares to add extra enum value, this code will still compile correctly!

Enough problems? Nope! I forgot break; in each case branch. Surprise.

An improvement is still possible to solve some of the problems above. Use return statement! So we have

Foo select(Bar bar)  switch(bar)  case Bar.VALUE: return value42(); case Bar.ELSE: return value444(); default: throw ThisCanNeverHappenException(); > > void action(Bar bar)  final Foo f = select(bar); doSomeMightyWork(f); >

Is it better now? More or less yes. But would you create an additional function for every switch ? I’m not sure.

When in Kotlin

The equivalent constuction to switch in Java is when in Kotlin. You may take a look to the when expression documentation for more details. Note, when expression is more functional than switch in Java.

fun action(bar: Bar)  var f : Foo when(bar)  Bar.VALUE -> f = value42() Bar.ELSE -> f = value444() else -> throw ThisCanNeverHappenException() > doSomeMightyWork(f) >

This was just one-to-one conversion to Kotlin and I see the warning to convert var f to val f at first.

It is good to notice, when can be used as expression! We may avoid assigning f variable inside each case.

The right of -> is also an expression. If you need more things to do, use < and >. There is no break exists or required.

If when is used as expression, else branch is not necessary, the compiler can prove all branches are included. At least this works if you checking enum or sealed classes. Compilation fails if a missing branch is detected.

Overall I turn the example into this:

void action(bar: Bar)  val f = when(bar)  Bar.VALUE -> value42(); Bar.ELSE -> value444(); > doSomeMightyWork(f); >

Generated bytecode

Let’s look into bytecode for the when statement call. Note. I use IntelliJ IDEA 2017.1 EAP with Kotlin 1.0.6 plugin. The generated bytecode may change with a future version of tools.

 // access flags 0x19 public final static action(LBar;)V @Lorg/jetbrains/annotations/NotNull;() // invisible, parameter 0 L0 ALOAD 0 LDC "e" INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull (Ljava/lang/Object;Ljava/lang/String;)V L1 LINENUMBER 13 L1 ALOAD 0 GETSTATIC WhKt$WhenMappings.$EnumSwitchMapping$0 : [I SWAP INVOKEVIRTUAL Bar.ordinal ()I IALOAD LOOKUPSWITCH 1: L2 2: L3 default: L4 L2 LINENUMBER 14 L2 INVOKESTATIC WhKt.value42 ()LFoo; GOTO L5 L3 LINENUMBER 15 L3 INVOKESTATIC WhKt.value444 ()LFoo; GOTO L5 L4 NEW kotlin/NoWhenBranchMatchedException DUP INVOKESPECIAL kotlin/NoWhenBranchMatchedException. ()V ATHROW L6 LINENUMBER 13 L6 L5 ASTORE 1 L7 LINENUMBER 18 L7 ALOAD 1 INVOKESTATIC WhKt.doSomeMightyWork (LFoo;)V L8 LINENUMBER 19 L8 RETURN L9 LOCALVARIABLE f LFoo; L7 L9 1 LOCALVARIABLE e LBar; L0 L9 0 MAXSTACK = 2 MAXLOCALS = 2

From the bytecode we see it throws kotlin/NoWhenBranchMatchedException in case it turned out there is an additional case. For example, this may happen if we are running a compiled code againt updated Bar enum with additional case added.

Still, a re-compilation will show there is an errors.

The only problem is that NoWhenBranchMatchedException contains no information on what kind of instance was there, maybe a toString() or getClass().getName() were nice to have helpers. Still, in general, such calls may also throw exceptions.

Conclusion

In this post we see how when expression can help one avoid trivial errors in switches. We discussed the benefit of using when as expression

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