Java constructor style: check parameters aren’t null
Here the exceptions let you know which parameter is null, but the constructor is now pretty ugly:, Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers ,Simple static methods to be called at the start of your own methods to verify correct arguments and state. This allows constructs such as,What are the best practices if you have a class which accepts some parameters but none of them are allowed to be null?
For less verbosity use Validate.notNull(obj, message) from commons-lang. Thus your constructor will look like:
public SomeClass(Object one, Object two)
Answer by Kyle Brown
Because it tells the user of your API what exactly went wrong.,The second or the third. ,It has checkNotNull that is used extensively within Guava. You can then write:,Simple static methods to be called at the start of your own methods to verify correct arguments and state. This allows constructs such as
For less verbosity use Validate.notNull(obj, message) from commons-lang. Thus your constructor will look like:
public SomeClass(Object one, Object two)
Java 7 added java.lang.Objects.requireNonNull() to the APIs everybody can use. So checking all arguments for null boils down to a short list like:
this.arg1 = Objects.requireNonNull(arg1, "arg1 must not be null"); this.arg2 = Objects.requireNonNull(arg2, "arg2 must not be null"); Simple static methods to be called at the start of your own methods to verify correct arguments and state. This allows constructs such as
to be replaced with the more compact
checkArgument(count > 0, "must be positive: %s", count); It has checkNotNull that is used extensively within Guava. You can then write:
import static com.google.common.base.Preconditions.checkNotNull; //. public SomeClass(Object one, Object two) < this.one = checkNotNull(one); this.two = checkNotNull(two, "two can't be null!"); //. > A NullPointerException isn’t reserved for just when you access members of a null reference; it’s pretty standard to throw them when an argument is null when that’s an illegal value.
System.out.println("some string".split(null)); // throws NullPointerException Answer by Tate Rice
Writing code to make sure that input parameters are not null does not make Java code «safer;» it’s exactly the opposite — it makes code less readable and less safe.,There is a somewhat prevalent notion that null-checks make Java code safer, but actually, it makes code less safe and less readable.,In a perfect world, it should not be possible to pass or return null values, at least not in public methods. This is one area where Kotlin, Haskell, and others are clearly better designed than Java. We can, however, pretend that nulls don’t exist. The question is: is that practical?,Checking for null parameters, however, is not the correct reaction to this admitted shortcoming of the type-system, because it ignores that there are actually two distinct categories of null-related issues.
It would be difficult to argue that null-checks are attractive. Most of the time, it’s just boilerplate code, which contributes nothing to the «logic» of the method. It is a purely technical construct. Like this one:
@Override public void getLock(String name, Handler> handler)
This method, from the otherwise very cool vert.x project, has three lines of code, two of which are checking for the null, so it makes this method somewhat harder to read. These sorts of checks are even more damaging when they actually contribute to the method’s logic:
@Override public Object getValue(final ELContext context, Object base, Object property)
@Override public void getLock(String name, Handler> handler)
@Override public void getLock(String name, Handler> handler)
This strategy, however, does not work if null is a legal value of some parameter or parameters. The simplest solution for these cases is to split the method into multiple ones with each requiring all its parameters. This would transform the Weld code above where the base parameter is not required:
public Object getValue(final ELContext context, Object base, Object property) // base not requiredpublic Object getObjectValue(final ELContext context, Object base, Object property) // base required . public Object getRootValue(final ELContext context, Object property) // base omittedRemoving these checks is only practical if the caller doesn’t have to check either. This is only possible if the caller can freely pass in results from other method calls. Therefore, methods shouldn’t return null. Every method that returns null legally needs to be changed depending on what meaning this null value carries. Most of the time, it means that a certain object could not be found and the caller should react according to its own logic. In these cases, the Optional class might help:
@Override public Optional getValue(final ELContext context, Object base, Object property)
Sometimes, returning null means that the caller should execute some default logic defined by the callee. Instead of pushing this responsibility to the caller, the method should return the default logic itself. Let’s take a look at an example from Weld again:
protected DisposalMethod resolveDisposalMethod(. ) < Set disposalBeans = . ; if (disposalBeans.size() == 1) < return disposalBeans.iterator().next(); >else if (disposalBeans.size() > 1) < throw . ; >return null; > One could think of this method returning null to indicate that there is no disposal method defined for a bean instantiated by Weld (a dependency injection framework). But actually, what this method wants to say is that there is nothing to do for disposal. Instead of legalizing null for a lot of intermediary objects, just so that some object can eventually check whether the returned DisposalMethod is null to do nothing, the method could just return a DisposalMethod that does nothing. Just have another implementation of it, like:
public final class NoDisposalMethod implements DisposalMethod < . @Override public void invoke(. ) < // Do nothing >>public final class NoDisposalMethod implements DisposalMethod < . @Override public void invoke(. ) < // Do nothing >>protected DisposalMethod resolveDisposalMethod(. )
Answer by Braylon Mills
In this tutorial, we’ll take a look at the need to check for null in Java and various alternatives that help us to avoid null checks in our code.,Here, we can use Java Assertions instead of the traditional null check conditional statement:,Generally, String validation includes a check for an empty value in addition to null value.,Using Optional with collections allows us to design APIs that are sure to return non-null values, thus avoiding explicit null checks on the client.
public void doSomething() < String result = doSomethingElse(); if (result.equalsIgnoreCase("Success")) // success >> private String doSomethingElse() Another common example is if we try to access a null array:
public static void main(String[] args) < findMax(null); >private static void findMax(int[] arr) < int max = arr[0]; //check other elements in loop >public void doSomething() < String result = doSomethingElse(); if (result != null && result.equalsIgnoreCase("Success")) < // success >else // failure > private String doSomethingElse() However, there are often APIs that can handle null values:
public void print(Object param) < System.out.println("Printing " + param); >public Object process() throws Exception < Object result = doSomething(); if (result == null) < throw new Exception("Processing fail. Got a null response"); >else < return result; >>public void accept(@NonNull Object param)
To add the support for these annotations in IntelliJ, we need to add the following Maven dependency:
org.jetbrains annotations 16.0.2 public void accept(Object param)
Let’s look at two methods — one that fails early and one that doesn’t:
public void goodAccept(String one, String two, String three) < if (one == null || two == null || three == null) < throw new IllegalArgumentException(); >process(one); process(two); process(three); > public void badAccept(String one, String two, String three) < if (one == null) < throw new IllegalArgumentException(); >else < process(one); >if (two == null) < throw new IllegalArgumentException(); >else < process(two); >if (three == null) < throw new IllegalArgumentException(); >else < process(three); >>Consider two implementations of a method that sums two integers:
public static int primitiveSum(int a, int b) < return a + b; >public static Integer wrapperSum(Integer a, Integer b)
Now let’s call these APIs in our client code:
int sum = primitiveSum(null, 2);And when using the API with wrapper classes, we get a NullPointerException:
assertThrows(NullPointerException.class, () -> wrapperSum(null, 2));Occasionally, we need to return a collection as a response from a method. For such methods, we should always try to return an empty collection instead of null:
public void accept(Object param) < Objects.requireNonNull(param); // doSomething() >Now let’s test the accept() method:
assertThrows(NullPointerException.class, () -> accept(null));Let’s see how Optional takes away the need for null checks:
public Optional process(boolean processed) < String response = doSomething(processed); if (response == null) < return Optional.empty(); >return Optional.of(response); > private String doSomething(boolean processed) < if (processed) < return "passed"; >else < return null; >>assertThrows(Exception.class, () -> process(false).orElseThrow(() -> new Exception()));To avoid this, Optional provides an ofNullable method that returns an Optional with the specified value, or empty, if the value is null:
public Optional process(boolean processed)
While dealing with empty collections, Optional comes in handy:
Alternatively, we can also allow the client to decide how to handle empty by returning Optional from this method:
public Optional findOptionalFirst()
Our findFirst method wants to return an Optional first element of an Optional list:
public Optional optionalListFirst() < return getOptionalList() .flatMap(list ->list.stream().findFirst()); >Before we move on to some examples, let’s add a Maven dependency for Lombok:
org.projectlombok lombok 1.18.20 Now we can use @NonNull wherever a null check is needed:
public void accept(@NonNull Object param)
So, we simply annotated the object for which the null check would’ve been required, and Lombok generates the compiled class:
public void accept(@NonNull Object param) < if (param == null) < throw new NullPointerException("param"); >else < System.out.println(param); >>Therefore, this would be a common validation statement:
public void accept(String param)
org.apache.commons commons-lang3 3.12.0 Let’s now refactor the above code with StringUtils:
public void accept(String param)
Answer by Brooks Calderon
You can use @NonNull on a record component, or a parameter of a method or constructor. This will cause to lombok generate a null-check statement for you. , If a null-check is already present at the top, no additional null-check will be generated. , A @NonNull on a primitive parameter results in a warning. No null-check will be generated. , Lombok has always treated various annotations generally named @NonNull on a field as a signal to generate a null-check if lombok generates an entire method or constructor for you, via for example @Data. However, using lombok’s own @lombok.NonNull on a parameter or record component results in the insertion of the null-check at the top of that method.
Answer by Aubree Montgomery
positional parameters are used in a similar to how you would use Java constructors, positional parameters are used in a similar to how you would use Java constructors ,1.4.2. Named parameters,Mixing named and positional parameters
class Foo < static int i >assert Foo.class.getDeclaredField('i').type == int.class assert Foo.i.class != int.class && Foo.i.class == Integer.classAnswer by Aurora Morton
Be consistent. When it comes to things like formatting, and casing, arguments about which is better are subjective and impossible to resolve. What we do know is that being consistent is objectively helpful.,Style Guide – This defines the rules for laying out and organizing code, or at least the parts that dart format doesn’t handle for you. The style guide also specifies how identifiers are formatted: camelCase, using_underscores, etc., Style Guide – This defines the rules for laying out and organizing code, or at least the parts that dart format doesn’t handle for you. The style guide also specifies how identifiers are formatted: camelCase, using_underscores, etc. ,For help on enabling linter rules, see the documentation for customizing static analysis.
Style Guide – This defines the rules for laying out and organizing code, or at least the parts that dart format doesn’t handle for you. The style guide also specifies how identifiers are formatted: camelCase , using_underscores , etc.
Style Guide – This defines the rules for laying out and organizing code, or at least the parts that dart format doesn’t handle for you. The style guide also specifies how identifiers are formatted: camelCase , using_underscores , etc.