java

How do you assert that a certain exception is thrown in JUnit tests?

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It depends on the JUnit version and what assert libraries you use. For JUnit5 and 4.13 see answer https://stackoverflow.com/a/2935935/2986984 If you use assertJ or google-truth, see answer https://stackoverflow.com/a/41019785/2986984 The original answer for JUnit <= 4.12 was: @Test(expected = IndexOutOfBoundsException.class) public void testIndexOutOfBoundsException() { ArrayList emptyList = new ArrayList(); Object o = emptyList.get(0); } Though answer … Read more

What is a JavaBean exactly?

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A JavaBean is just a standard. It is a regular Java class, except it follows certain conventions: All properties are private (use getters/setters) A public no-argument constructor Implements Serializable. That’s it. It’s just a convention. Lots of libraries depend on it though. With respect to Serializable, from the API documentation: Serializability of a class is … Read more

How to get an enum value from a string value in Java

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Yes, Blah.valueOf(“A”) will give you Blah.A. Note that the name must be an exact match, including case: Blah.valueOf(“a”) and Blah.valueOf(“A “) both throw an IllegalArgumentException. The static methods valueOf() and values() are created at compile time and do not appear in source code. They do appear in Javadoc, though; for example, Dialog.ModalityType shows both methods.

What’s the simplest way to print a Java array?

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Since Java 5 you can use Arrays.toString(arr) or Arrays.deepToString(arr) for arrays within arrays. Note that the Object[] version calls .toString() on each object in the array. The output is even decorated in the exact way you’re asking. Examples: Simple Array: String[] array = new String[] {“John”, “Mary”, “Bob”}; System.out.println(Arrays.toString(array)); Output: [John, Mary, Bob] Nested Array: … Read more

“implements Runnable” vs “extends Thread” in Java

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Yes: implements Runnable is the preferred way to do it, IMO. You’re not really specialising the thread’s behaviour. You’re just giving it something to run. That means composition is the philosophically “purer” way to go. In practical terms, it means you can implement Runnable and extend from another class as well… and you can also … Read more

What’s the difference between @Component, @Repository & @Service annotations in Spring?

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From Spring Documentation: The @Repository annotation is a marker for any class that fulfils the role or stereotype of a repository (also known as Data Access Object or DAO). Among the uses of this marker is the automatic translation of exceptions, as described in Exception Translation. Spring provides further stereotype annotations: @Component, @Service, and @Controller. … Read more

How do I determine whether an array contains a particular value in Java?

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Arrays.asList(yourArray).contains(yourValue) Warning: this doesn’t work for arrays of primitives (see the comments). Since java-8 you can now use Streams. String[] values = {“AB”,”BC”,”CD”,”AE”}; boolean contains = Arrays.stream(values).anyMatch(“s”::equals); To check whether an array of int, double or long contains a value use IntStream, DoubleStream or LongStream respectively. Example int[] a = {1,2,3,4}; boolean contains = IntStream.of(a).anyMatch(x … Read more

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