[JAVA-621] Flattened modules hierarchy
This commit is contained in:
dupirefr
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## Core Java Lang OOP - Constructors
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This module contains article about constructors in Java
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### Relevant Articles:
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- [A Guide to Constructors in Java](https://www.baeldung.com/java-constructors)
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- [Java Copy Constructor](https://www.baeldung.com/java-copy-constructor)
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- [Cannot Reference “X” Before Supertype Constructor Has Been Called](https://www.baeldung.com/java-cannot-reference-x-before-supertype-constructor-error)
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28
core-java-modules/core-java-lang-oop-constructors/pom.xml
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28
core-java-modules/core-java-lang-oop-constructors/pom.xml
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>core-java-modules</artifactId>
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<groupId>com.baeldung.core-java-modules</groupId>
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<version>1.0.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>core-java-lang-oop-constructors</artifactId>
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<name>core-java-lang-oop-constructors</name>
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<packaging>jar</packaging>
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<dependencies>
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<dependency>
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<groupId>org.assertj</groupId>
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<artifactId>assertj-core</artifactId>
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<version>${assertj-core.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<properties>
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<assertj-core.version>3.10.0</assertj-core.version>
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</properties>
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</project>
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package com.baeldung.constructors;
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import java.time.LocalDateTime;
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class BankAccount {
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String name;
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LocalDateTime opened;
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double balance;
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@Override
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public String toString() {
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return String.format("%s, %s, %f", this.name, this.opened.toString(), this.balance);
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}
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public String getName() {
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return name;
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}
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public LocalDateTime getOpened() {
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return opened;
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}
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public double getBalance() {
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return this.balance;
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}
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}
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class BankAccountEmptyConstructor extends BankAccount {
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public BankAccountEmptyConstructor() {
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this.name = "";
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this.opened = LocalDateTime.now();
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this.balance = 0.0d;
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}
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}
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class BankAccountParameterizedConstructor extends BankAccount {
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public BankAccountParameterizedConstructor(String name, LocalDateTime opened, double balance) {
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this.name = name;
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this.opened = opened;
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this.balance = balance;
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}
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}
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class BankAccountCopyConstructor extends BankAccount {
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public BankAccountCopyConstructor(String name, LocalDateTime opened, double balance) {
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this.name = name;
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this.opened = opened;
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this.balance = balance;
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}
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public BankAccountCopyConstructor(BankAccount other) {
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this.name = other.name;
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this.opened = LocalDateTime.now();
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this.balance = 0.0f;
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}
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}
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class BankAccountChainedConstructors extends BankAccount {
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public BankAccountChainedConstructors(String name, LocalDateTime opened, double balance) {
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this.name = name;
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this.opened = opened;
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this.balance = balance;
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}
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public BankAccountChainedConstructors(String name) {
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this(name, LocalDateTime.now(), 0.0f);
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}
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}
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package com.baeldung.constructors;
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import java.time.LocalDateTime;
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class Transaction {
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final BankAccountEmptyConstructor bankAccount;
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final LocalDateTime date;
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final double amount;
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public Transaction(BankAccountEmptyConstructor account, LocalDateTime date, double amount) {
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this.bankAccount = account;
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this.date = date;
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this.amount = amount;
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}
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/*
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* Compilation Error :'(, all final variables must be explicitly initialised.
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* public Transaction() {
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* }
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*/
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public void invalidMethod() {
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// this.amount = 102.03; // Results in a compiler error. You cannot change the value of a final variable.
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}
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}
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package com.baeldung.copyconstructor;
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import java.util.Date;
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public class Employee {
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protected int id;
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protected String name;
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protected Date startDate;
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public Employee(int id, String name, Date startDate) {
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this.id = id;
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this.name = name;
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this.startDate = startDate;
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}
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public Employee(Employee employee) {
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this.id = employee.id;
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this.name = employee.name;
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this.startDate = new Date(employee.startDate.getTime());
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}
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Date getStartDate() {
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return startDate;
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}
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public Employee copy() {
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return new Employee(this);
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}
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}
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package com.baeldung.copyconstructor;
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import java.util.Date;
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import java.util.List;
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import java.util.stream.Collectors;
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public class Manager extends Employee {
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private List<Employee> directReports;
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public Manager(int id, String name, Date startDate, List<Employee> directReports) {
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super(id, name, startDate);
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this.directReports = directReports;
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}
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public Manager(Manager manager) {
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super(manager.id, manager.name, manager.startDate);
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this.directReports = manager.directReports.stream()
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.collect(Collectors.toList());
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}
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@Override
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public Employee copy() {
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return new Manager(this);
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}
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List<Employee> getDirectReport() {
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return this.directReports;
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}
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}
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package com.baeldung.supertypecompilerexception;
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public class MyClass {
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private int myField1 = 10;
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private int myField2;
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public MyClass() {
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//uncomment this to see the supertype compiler error:
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//this(myField1);
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}
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public MyClass(int i) {
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myField2 = i;
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}
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}
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package com.baeldung.supertypecompilerexception;
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public class MyClassSolution1 {
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private int myField1 = 10;
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private int myField2;
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public MyClassSolution1() {
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myField2 = myField1;
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}
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public MyClassSolution1(int i) {
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myField2 = i;
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}
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}
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package com.baeldung.supertypecompilerexception;
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public class MyClassSolution2 {
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private int myField1 = 10;
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private int myField2;
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public MyClassSolution2() {
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setupMyFields(myField1);
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}
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public MyClassSolution2(int i) {
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setupMyFields(i);
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}
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private void setupMyFields(int i) {
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myField2 = i;
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}
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}
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package com.baeldung.supertypecompilerexception;
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public class MyClassSolution3 {
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private static final int SOME_CONSTANT = 10;
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private int myField2;
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public MyClassSolution3() {
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this(SOME_CONSTANT);
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}
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public MyClassSolution3(int i) {
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myField2 = i;
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}
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}
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package com.baeldung.supertypecompilerexception;
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public class MyException extends RuntimeException {
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private int errorCode = 0;
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public MyException(String message) {
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//uncomment this to see the supertype compiler error:
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//super(message + getErrorCode());
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}
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public int getErrorCode() {
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return errorCode;
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}
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}
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package com.baeldung.constructors;
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import org.assertj.core.api.Assertions;
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import org.junit.Test;
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import java.time.LocalDateTime;
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import java.time.Month;
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import static org.assertj.core.api.Assertions.assertThat;
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public class ConstructorUnitTest {
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@Test
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public void givenNoExplicitContructor_whenUsed_thenFails() {
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BankAccount account = new BankAccount();
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Assertions.assertThatThrownBy(() -> {
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account.toString();
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}).isInstanceOf(Exception.class);
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}
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@Test
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public void givenNoArgumentConstructor_whenUsed_thenSucceeds() {
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BankAccountEmptyConstructor account = new BankAccountEmptyConstructor();
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Assertions.assertThatCode(() -> {
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account.toString();
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}).doesNotThrowAnyException();
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}
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@Test
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public void givenParameterisedConstructor_whenUsed_thenSucceeds() {
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LocalDateTime opened = LocalDateTime.of(2018, Month.JUNE, 29, 06, 30, 00);
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BankAccountParameterizedConstructor account =
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new BankAccountParameterizedConstructor("Tom", opened, 1000.0f);
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Assertions.assertThatCode(() -> {
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account.toString();
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}).doesNotThrowAnyException();
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}
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@Test
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public void givenCopyContructor_whenUser_thenMaintainsLogic() {
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LocalDateTime opened = LocalDateTime.of(2018, Month.JUNE, 29, 06, 30, 00);
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BankAccountCopyConstructor account = new BankAccountCopyConstructor("Tim", opened, 1000.0f);
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BankAccountCopyConstructor newAccount = new BankAccountCopyConstructor(account);
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assertThat(account.getName()).isEqualTo(newAccount.getName());
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assertThat(account.getOpened()).isNotEqualTo(newAccount.getOpened());
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assertThat(newAccount.getBalance()).isEqualTo(0.0f);
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}
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@Test
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public void givenChainedConstructor_whenUsed_thenMaintainsLogic() {
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BankAccountChainedConstructors account = new BankAccountChainedConstructors("Tim");
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BankAccountChainedConstructors newAccount = new BankAccountChainedConstructors("Tim", LocalDateTime.now(), 0.0f);
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assertThat(account.getName()).isEqualTo(newAccount.getName());
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assertThat(account.getBalance()).isEqualTo(newAccount.getBalance());
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}
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}
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package com.baeldung.copyconstructor;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertNotEquals;
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import java.util.Date;
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import org.junit.Test;
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public class EmployeeUnitTest {
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@Test
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public void givenCopyConstructor_whenDeepCopy_thenDistinct() {
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Date d1 = new Date(123);
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Employee e1 = new Employee(1, "Baeldung", d1);
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Employee e2 = new Employee(e1);
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assertEquals(d1, e1.getStartDate());
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assertEquals(d1, e2.getStartDate());
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d1.setTime(456);
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assertEquals(d1, e1.getStartDate());
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assertNotEquals(d1, e2.getStartDate());
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}
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@Test
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public void givenCopyMethod_whenCopy_thenDistinct() {
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Date d1 = new Date(123);
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Employee e1 = new Employee(1, "Baeldung", d1);
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Employee e2 = e1.copy();
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assertEquals(d1, e1.getStartDate());
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assertEquals(d1, e2.getStartDate());
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d1.setTime(456);
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assertEquals(d1, e1.getStartDate());
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assertNotEquals(d1, e2.getStartDate());
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}
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}
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package com.baeldung.copyconstructor;
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import static org.junit.Assert.assertArrayEquals;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertTrue;
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import java.util.ArrayList;
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import java.util.Date;
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import java.util.List;
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import org.junit.Test;
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public class ManagerUnitTest {
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@Test
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public void givenCopyConstructor_whenDeepCopy_thenDistinct() {
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Date startDate = new Date(123);
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Employee e1 = new Employee(1, "Baeldung", startDate);
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Employee e2 = new Employee(e1);
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List<Employee> directReports = new ArrayList<Employee>();
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directReports.add(e1);
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directReports.add(e2);
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Manager m1 = new Manager(1, "Baeldung Manager", startDate, directReports);
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Manager m2 = new Manager(m1);
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List<Employee> directReports1 = m1.getDirectReport();
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List<Employee> directReports2 = m2.getDirectReport();
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assertEquals(directReports1.size(), directReports2.size());
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assertArrayEquals(directReports1.toArray(), directReports2.toArray());
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// clear m1's direct reports list. m2's list should not be affected
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directReports.clear();
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directReports1 = m1.getDirectReport();
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directReports2 = m2.getDirectReport();
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assertEquals(0, directReports1.size());
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assertEquals(2, directReports2.size());
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}
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@Test
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public void givenCopyMethod_whenCopy_thenDistinct() {
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Date startDate = new Date(123);
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Employee e1 = new Employee(1, "Baeldung", startDate);
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Employee e2 = new Employee(e1);
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List<Employee> directReports = new ArrayList<Employee>();
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directReports.add(e1);
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directReports.add(e2);
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// a Manager object whose declaration type is Employee.
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Employee source = new Manager(1, "Baeldung Manager", startDate, directReports);
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Employee clone = source.copy();
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// after copy, clone should be still a Manager object.
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assertTrue(clone instanceof Manager);
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List<Employee> directReports1 = ((Manager) source).getDirectReport();
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List<Employee> directReports2 = ((Manager) clone).getDirectReport();
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assertEquals(directReports1.size(), directReports2.size());
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assertArrayEquals(directReports1.toArray(), directReports2.toArray());
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// clear source's direct reports list. clone's list should not be affected
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directReports.clear();
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directReports1 = ((Manager) source).getDirectReport();
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directReports2 = ((Manager) clone).getDirectReport();
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assertEquals(0, directReports1.size());
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assertEquals(2, directReports2.size());
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}
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}
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Reference in New Issue
Block a user