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[JAVA-621] core-java-lang-oop-methods module

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* Creation

* Moved code from https://www.baeldung.com/java-equals-hashcode-contracts

* Moved code from www.baeldung.com/java-hashcode

* Moved code from https://www.baeldung.com/java-method-overload-override

* Moved code from www.baeldung.com/java-methods

* Moved article references to the new README.md
This commit is contained in:
dupirefr
2020-04-04 11:38:22 +02:00
parent 21a98198b6
commit 867d63a9d5
23 changed files with 45 additions and 4 deletions
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1
core-java-modules/core-java-lang-oop-2/README.md
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@@ -3,5 +3,4 @@
This module contains articles about Object-oriented programming (OOP) in Java
### Relevant Articles:
- [Java equals() and hashCode() Contracts](https://www.baeldung.com/java-equals-hashcode-contracts)
- [[<-- Prev]](/core-java-modules/core-java-lang-oop)[[More -->]](/core-java-modules/core-java-lang-oop-3)

36
core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/equalshashcode/Money.java
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@@ -1,36 +0,0 @@
package com.baeldung.equalshashcode;
class Money {
int amount;
String currencyCode;
Money(int amount, String currencyCode) {
this.amount = amount;
this.currencyCode = currencyCode;
}
@Override
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Money))
return false;
Money other = (Money)o;
boolean currencyCodeEquals = (this.currencyCode == null && other.currencyCode == null)
|| (this.currencyCode != null && this.currencyCode.equals(other.currencyCode));
return this.amount == other.amount
&& currencyCodeEquals;
}
@Override
public int hashCode() {
int result = 17;
result = 31 * result + amount;
if (currencyCode != null) {
result = 31 * result + currencyCode.hashCode();
}
return result;
}
}

39
core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/equalshashcode/Team.java
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@@ -1,39 +0,0 @@
package com.baeldung.equalshashcode;
class Team {
final String city;
final String department;
Team(String city, String department) {
this.city = city;
this.department = department;
}
@Override
public final boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Team))
return false;
Team otherTeam = (Team)o;
boolean cityEquals = (this.city == null && otherTeam.city == null)
|| this.city != null && this.city.equals(otherTeam.city);
boolean departmentEquals = (this.department == null && otherTeam.department == null)
|| this.department != null && this.department.equals(otherTeam.department);
return cityEquals && departmentEquals;
}
@Override
public final int hashCode() {
int result = 17;
if (city != null) {
result = 31 * result + city.hashCode();
}
if (department != null) {
result = 31 * result + department.hashCode();
}
return result;
}
}

38
core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/equalshashcode/Voucher.java
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@@ -1,38 +0,0 @@
package com.baeldung.equalshashcode;
class Voucher {
private Money value;
private String store;
Voucher(int amount, String currencyCode, String store) {
this.value = new Money(amount, currencyCode);
this.store = store;
}
@Override
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Voucher))
return false;
Voucher other = (Voucher)o;
boolean valueEquals = (this.value == null && other.value == null)
|| (this.value != null && this.value.equals(other.value));
boolean storeEquals = (this.store == null && other.store == null)
|| (this.store != null && this.store.equals(other.store));
return valueEquals && storeEquals;
}
@Override
public int hashCode() {
int result = 17;
if (this.value != null) {
result = 31 * result + value.hashCode();
}
if (this.store != null) {
result = 31 * result + store.hashCode();
}
return result;
}
}

30
core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/equalshashcode/WrongTeam.java
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@@ -1,30 +0,0 @@
package com.baeldung.equalshashcode;
/* (non-Javadoc)
* This class overrides equals, but it doesn't override hashCode.
*
* To see which problems this leads to:
* TeamUnitTest.givenMapKeyWithoutHashCode_whenSearched_thenReturnsWrongValue
*/
class WrongTeam {
String city;
String department;
WrongTeam(String city, String department) {
this.city = city;
this.department = department;
}
@Override
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof WrongTeam))
return false;
WrongTeam otherTeam = (WrongTeam)o;
return this.city == otherTeam.city
&& this.department == otherTeam.department;
}
}

47
core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/equalshashcode/WrongVoucher.java
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@@ -1,47 +0,0 @@
package com.baeldung.equalshashcode;
/* (non-Javadoc)
* This class extends the Money class that has overridden the equals method and once again overrides the equals method.
*
* To see which problems this leads to:
* MoneyUnitTest.givenMoneyAndVoucherInstances_whenEquals_thenReturnValuesArentSymmetric
*/
class WrongVoucher extends Money {
private String store;
WrongVoucher(int amount, String currencyCode, String store) {
super(amount, currencyCode);
this.store = store;
}
@Override
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof WrongVoucher))
return false;
WrongVoucher other = (WrongVoucher)o;
boolean currencyCodeEquals = (this.currencyCode == null && other.currencyCode == null)
|| (this.currencyCode != null && this.currencyCode.equals(other.currencyCode));
boolean storeEquals = (this.store == null && other.store == null)
|| (this.store != null && this.store.equals(other.store));
return this.amount == other.amount
&& currencyCodeEquals
&& storeEquals;
}
@Override
public int hashCode() {
int result = 17;
result = 31 * result + amount;
if (this.currencyCode != null) {
result = 31 * result + currencyCode.hashCode();
}
if (this.store != null) {
result = 31 * result + store.hashCode();
}
return result;
}
}

27
core-java-modules/core-java-lang-oop-2/src/test/java/com/baeldung/equalshashcode/MoneyUnitTest.java
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@@ -1,27 +0,0 @@
package com.baeldung.equalshashcode;
import org.junit.Test;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
public class MoneyUnitTest {
@Test
public void givenMoneyInstancesWithSameAmountAndCurrency_whenEquals_thenReturnsTrue() {
Money income = new Money(55, "USD");
Money expenses = new Money(55, "USD");
assertTrue(income.equals(expenses));
}
@Test
public void givenMoneyAndVoucherInstances_whenEquals_thenReturnValuesArentSymmetric() {
Money cash = new Money(42, "USD");
WrongVoucher voucher = new WrongVoucher(42, "USD", "Amazon");
assertFalse(voucher.equals(cash));
assertTrue(cash.equals(voucher));
}
}

45
core-java-modules/core-java-lang-oop-2/src/test/java/com/baeldung/equalshashcode/TeamUnitTest.java
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@@ -1,45 +0,0 @@
package com.baeldung.equalshashcode;
import nl.jqno.equalsverifier.EqualsVerifier;
import org.junit.Test;
import java.util.HashMap;
import java.util.Map;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
public class TeamUnitTest {
@Test
public void givenMapKeyWithHashCode_whenSearched_thenReturnsCorrectValue() {
Map<Team,String> leaders = new HashMap<>();
leaders.put(new Team("New York", "development"), "Anne");
leaders.put(new Team("Boston", "development"), "Brian");
leaders.put(new Team("Boston", "marketing"), "Charlie");
Team myTeam = new Team("New York", "development");
String myTeamleader = leaders.get(myTeam);
assertEquals("Anne", myTeamleader);
}
@Test
public void givenMapKeyWithoutHashCode_whenSearched_thenReturnsWrongValue() {
Map<WrongTeam,String> leaders = new HashMap<>();
leaders.put(new WrongTeam("New York", "development"), "Anne");
leaders.put(new WrongTeam("Boston", "development"), "Brian");
leaders.put(new WrongTeam("Boston", "marketing"), "Charlie");
WrongTeam myTeam = new WrongTeam("New York", "development");
String myTeamleader = leaders.get(myTeam);
assertFalse("Anne".equals(myTeamleader));
}
@Test
public void equalsContract() {
EqualsVerifier.forClass(Team.class).verify();
}
}