Programo IssuesProgramo Issues

Cora Pérez Ariza ~ DECSAI ~ UGR

Granada, January 28th & 29th, 2009

IndexIndex

JUnit◦Introduction to the topic◦Tags◦Example

Design Decisions◦equals and hashCode methods◦toString method

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JUnitIntroduction

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Why a JUnit?They reassure us that the expected behavior of our

work is the actual behavior (and will stay like that in the future)

How to use it?• Creation is easy: short methods that test critical

parts of the project’s classes.• Integrated on NetBeans• Few “tags” to learn

JUnitTags

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Tags:

• @Test

• @Before and @After

• @BeforeClass and @AfterClass

• @Ignore

JUnitExample: Beginning

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package programo.core.potential;

import org.junit.After;import org.junit.AfterClass;import org.junit.Before;import org.junit.BeforeClass;import org.junit.Test;import org.junit.Ignore;import static org.junit.Assert.*;

import programo.core.variable.*;import programo.core.assignation.*;

You should import as many classes as tags you are going to use

JUnitExample: data members

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public class PotentialTableTest {

PotentialTable pot1, pot2, resNorm, resMarg, resComb, resProj; CategoricalVariable X1, X2, X3, X4; CategoricalAssignation configurationToProject; VariableSet setOfVars1, setOfVars2;

You can declare variables as class members, to use as global variables for your tests

JUnitExample: before/after the tests

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@BeforeClass public static void setUpClass() throws Exception { …. }

@AfterClass public static void tearDownClass() throws Exception { … }

These methods will run before/after the bunch of tests (only once)

JUnitExample: before/after each test

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@Before public void setUp() { … }

@After public void tearDown() { … }

These methods will run before/after each test (so one time per test)

JUnitExample: auxiliar methods

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public void initializeVariables(){ …}

You can define auxiliar methods to perform specific operations within your JUnit file

JUnitExample: test cases

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@Testpublic void testNormalizePotential() {

initializeVariables();

pot1.normalizePotential();

assertTrue(resNorm.equalValues(pot1));

}

@Test tag marks the method as a test

Body of the test case

Assertion to check if the test has worked

JUnitExample: test cases

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@Ignore("Not ready to run")@Testpublic void testSumMarginalize() {

initializeVariables();

Potential result = pot1.sumMarginalize(setOfVars2);

assertTrue(resMarg.equalValues(result));

}

You may not want to execute one or more test cases: use @Ignore

JUnitResult in NetBeans

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JUnitOther useful utilities

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Other utilities:

• Exception Handling• Use “expected” parameter with @Test tag for

test cases that expect exception:• @Test(expected = ArithmeticException.class)

• Timeout• Define a timeout period in miliseconds:

• @Test(timeout = 1000)

Design DecisionsOverview: equals General Contract

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public boolean equals(Object obj):• Implements an equivalence relation:

• It is reflexiveo For any reference value x, x.equals(x) should return true

• It is symmetrico For any x and y, x.equals(y) == y.equals(x)

• It is transitiveo For any x, y, z, if x.equals(y) and y.equals(z), then x.equals(z)

• It is consistento For any x and y, x.equals(y) should return the same in every

invocation if both remains inmutable• For any non-null reference value x, x.equals(null) should return

false• Equal objects must have equal hash codes

Design DecisionsOverview: hashCode General Contract

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public int hashCode():

• Must be consistent during the same execution of the application

• Equal objects must produce equal hash codes, however unequal objects need not produce distinct hash codesoDifferent hash codes for different objects may

improve the performance of hashtables

Design Decisionsequals and hashCode: when to override

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Do not override:• Each instance of the class is inherently unique• You don’t care whether the class provides a “logical equality”

test• A super class has already overridden equals appropriately for

this class• The class is private or package private, and you are certain that

its equals method will never be invoked

Override:• When a class has a notion of logical equality that differs from

mere object identity, and a super class has not already overridden equals to implement the desired behavior

Design Decisionsequals and hashCode: possible problems

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Problems with sets and hash maps:

Overriding equals enables instances of the class to serve as map keys or set elements with predictable, desirable behavior

Design Decisionsequals and hashCode: possible problems: Example

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Problems with sets and hash maps: public class Point{ private final int x; private final int y; public Point(int x, int y){ this.x = x; this.y = y; }}

… HashMap tabla = new HashMap(); tabla.put(new Point(1,3), 1);if(tabla.containsKey(new Point(1,3))) System.out.println("both points are the same");else System.out.println("two different objects");

Design Decisionsequals and hashCode: possible problems: Example

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Problems with sets and hash maps:public class Point{ private final int x; private final int y; public Point(int x, int y){ this.x = x; this.y = y; } @Override public boolean equals(Object obj){ if(this == obj) return true; if(obj == null) || (obj.getClass() != this.getClass()) return false; Point p = (Point) obj; return (p.x == this.x && p.y == this.y) }}

Design Decisionsequals and hashCode: possible problems: Example

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Problems with sets and hash maps:

Design Decisionsequals and hashCode: general advice

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equals:• Do not change the type of the argument, it takes java.lang.Object• Review your method to verify that it fulfills all the requirements stated

by the general contract• Do not forget to override hashCode method whenever you override

equals method• Primitives can be compared directly with equality operator (==)

• float to Float.floatToIntBits• double to Double.doubleToLongBits

• instance of VS getClass• Instance of checks if same class or subclass

• May break symmetry requirement• Use only if class final

• getClass checks if same class exclusively

Design Decisionsequals and hashCode: general advice

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hashCode:

• Involve significant variables of your object in the calculation of the hash code

• Review your hashCode method and check if it is returning equal hash codes for equals objects

• Different hash codes for different objects is not mandatory, but advisable

Design Decisionsequals method in ProGraMo

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When should two objects be equals?

• When they refer to the same object?• Shallow comparison

• When although they are different objects, their data members’ values are the same?• Deep comparison

Design DecisionstoString method

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We should always override toString()

• Providing a good toString implementation makes a class much more pleasant to use

• toString method should return all of the interesting information contained in the object

Thanks!Thanks!DECSAI ~ UGR

“Effective Java”, by Joshua Bloch. Addison Wesley

“Equals and HashCode”, by Manish Hatwalnehttp://www.geocities.com/technofundo/tech/java/equalhash.html

“Junit 4 in 60 Seconds”, by cavdar.nethttp://www.cavdar.net/2008/07/21/junit-4-in-60-seconds/