[In-house study session] Basics of Java annotation (2017/11/02) ~ Under construction ~

0. Introduction

Contents

• Annotation basics.

Prerequisite knowledge

• Java basic syntax
• How to use Java annotations

Reference books

"Effective Java 2nd Edition" Maruzen Publishing

table of contents

1. Benefits of annotation
2. Self-made annotation
3. View the contents of JUnit, lombok

1. Benefits of annotation

Java Annotation Overview

Annotation (English: annotation) is to add related information (metadata) to a certain data as an annotation.

• [Annotation-Wikipedia](https://ja.wikipedia.org/wiki/%E3%82%A2%E3%83%8E%E3%83%86%E3%83%BC%E3%82%B7% E3% 83% A7% E3% 83% B3) Quote

• Introduced from Java 5 (released in 2004)

Annotation example (JUnit4)

CalculationTest.java

public class CalculationTest {
    /**Test case 1*/
	@Test
	public void sampleTest1() {
		//...
	}
    /**Test case 2*/
	@Test
	public void sampleTest2() {
		//...
	}    
}

• Express as a test case with @Test
• JUnit Runner only executes methods with @Test
• Annotations were introduced from JUnit4

If you can't use annotations in JUnit (JUnit3)

CalculationTest.java

public class CalculationTest extends TestCase{
    /**Test case 1*/
	public void testSample1() {
		//...
	}
    /**Test case 2*/
	public void testSample2() {
		//...
	}    
}

• Indicates that it is a test class by inheriting TestCase

• Method names that become test cases start with test ⇒ Naming pattern

• Http://d.hatena.ne.jp/smada564/20110501/1304265351 Reference

Disadvantages of naming patterns

Don't notice the typo

• If the method has the name tsetSample2 (typo), it just won't be executed. No error

Parameter values cannot be associated

For example, consider a test method that expects to throw ʻIllegalArgumentException`.

/**How to write JUnit4*/
@Test(expected = IllegalArgumentException.class)
public void sample() {
	//...
}

/**Example when annotation cannot be used*/
public void test_IllegalArgumentException_sample() {
	//...
}    

• Ugly and vulnerable

• Compile cannot determine if an Exception exists --I don't notice until I run it

• "Effective Java 2nd Edition" Item 35 Reference

Comparison of XML and annotation

Servlet can be set with either annotation or XML.

@WebServlet("/Hello")
public class HelloServlet extends HttpServlet {
  //...
}

web.xml

<!--If not use annotation, specify in XML-->
<servlet>
  <servlet-name>Hello</servlet-name>
  <servlet-class>jp.co.sample.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>Hello</servlet-name>
  <url-pattern>/Hello</url-pattern>
</servlet-mapping>

Annotation features compared to XML

• Small amount of description
• Completed in one file
• Even if you change the class name or method name, you do not need to modify the annotation.

⇒ ** Strong against source changes **

• Annotations vs XML, advantages and disadvantages Reference

Standard library annotation

@Override

Annotation indicating that the method is overridden.

Book.java

public class Book {
	public Book(String title, String author) {
		this.title = title;
		this.author = author;
	}
	String title;
	String author;

	@Override //Compile Error.Correctly equals(Object obj)
	public boolean equals(Book obj) {
		//Null check omitted
		return title.equals(obj.title) && author.equals(obj.author);
	}

}

At compile time, notice that it is not overriding (overloaded).

• "Effective Java 2nd Edition" Item 36 Reference
• [Effective Java] Item 36: Always use Override annotation Reference

@Deprecated

From Java9, you can write @Deprecated (since =" 9 ", forRemoval = true).

• Is it going to be abolished? (forRemoval)

• When will it be abolished? (since)

• What ’s New for Core Libraries in JDK Reference

@SuppressWarnings

Make the IDE suppress warning messages.

@SuppressWarnings( "unchecked" ) //Exclude warnings about type checking
@SuppressWarnings( "javadoc" ) //JavaDoc warning exclusion
public class Book {
	//..
}

• Http://capm-network.com/?tag=Java-%E3%82%A2%E3%83%8E%E3%83%86%E3%83%BC%E3%82%B7%E3%83 See% A7% E3% 83% B3

value attribute

appendix

Standard annotation

Reference site

http://www.oracle.com/webfolder/technetwork/jp/javamagazine/Java-MA14-Architect-TypeAnnotations.pdf http://www.oracle.com/webfolder/technetwork/jp/javamagazine/Java-MA16-Annotations.pdf