Java 编程简介，第 2 部分: 构建真实的应用程序

public void printAudit(StringBuilder buffer) {   buffer.append("Name="); buffer.append(getName());   buffer.append(","); buffer.append("Age="); buffer.append(getAge());   buffer.append(","); buffer.append("Height="); buffer.append(getHeight());   buffer.append(","); buffer.append("Weight="); buffer.append(getWeight());   buffer.append(","); buffer.append("EyeColor="); buffer.append(getEyeColor());   buffer.append(","); buffer.append("Gender="); buffer.append(getGender()); } public void printAudit(Logger l) {   StringBuilder sb = new StringBuilder();   printAudit(sb);   l.info(sb.toString()); }

package com.makotojava.intro;  public class Employee extends Person {    public Employee() {     super();     // TODO Auto-generated constructor stub   }      public Employee(String name, int age, int height, int weight,   String eyeColor, String gender) {     super(name, age, height, weight, eyeColor, gender);     // TODO Auto-generated constructor stub   }  }

package com.makotojava.intro;  import java.math.BigDecimal;  public class Employee extends Person {    private String taxpayerIdentificationNumber;   private String employeeNumber;   private BigDecimal salary;    public Employee() {     super();   }   public String getTaxpayerIdentificationNumber() {     return taxpayerIdentificationNumber;   }   public void setTaxpayerIdentificationNumber(String taxpayerIdentificationNumber) {     this.taxpayerIdentificationNumber = taxpayerIdentificationNumber;   }    // Other getter/setters... }

@Override public void printAudit(StringBuilder buffer) {   // Call the superclass version of this method first to get its attribute values   super.printAudit(buffer);   // Now format this instance's values   buffer.append("TaxpayerIdentificationNumber=");   buffer.append(getTaxpayerIdentificationNumber());   buffer.append(","); buffer.append("EmployeeNumber=");   buffer.append(getEmployeeNumber());   buffer.append(","); buffer.append("Salary=");   buffer.append(getSalary().setScale(2).toPlainString()); }

accessSpecifier static variableName [= initialValue];

public class Person {   //...   public static final String GENDER_MALE = "MALE";   public static final String GENDER_FEMALE = "FEMALE";   // ...   public static void main(String[] args) {   Person p = new Person("Joe Q Author", 42, 173, 82, "Brown", GENDER_MALE);     // ...   }   //... }

String genderValue = Person.GENDER_MALE;

public class Employee extends Person {   private static final Logger logger = Logger.getLogger(Employee.class.getName());   //...   public static Logger getLogger() {     return logger;   }  }

Logger employeeLogger = Employee.getLogger();

public class EmployeeTest {   @Test   public void test() {     int int1 = 1;     int int2 = 1;     Logger l = Logger.getLogger(EmployeeTest.class.getName());          l.info("Q: int1 == int2?           A:" + (int1 == int2));     Integer integer1 = Integer.valueOf(int1);     Integer integer2 = Integer.valueOf(int2);     l.info("Q:Integer1 == Integer2?   A:" + (integer1 == integer2));     integer1 = new Integer(int1);     integer2 = new Integer(int2);     l.info("Q:Integer1 == Integer2?   A:" + (integer1 == integer2));     Employee employee1 = new Employee();     Employee employee2 = new Employee();     l.info("Q:Employee1 == Employee2?A:" + (employee1 == employee2));   } }

Sep 18, 2015 5:09:56 PM com.makotojava.intro.EmployeeTest test INFO:Q: int1 == int2?           A: true Sep 18, 2015 5:09:56 PM com.makotojava.intro.EmployeeTest test INFO:Q:Integer1 == Integer2?   A: true Sep 18, 2015 5:09:56 PM com.makotojava.intro.EmployeeTest test INFO:Q:Integer1 == Integer2?   A: false Sep 18, 2015 5:09:56 PM com.makotojava.intro.EmployeeTest test INFO:Q:Employee1 == Employee2?A: false

a.equals(b);

@Test public void anotherTest() {   Logger l = Logger.getLogger(Employee.class.getName());   Integer integer1 = Integer.valueOf(1);   Integer integer2 = Integer.valueOf(1);   l.info("Q: integer1 == integer2 ?A:" + (integer1 == integer2));   l.info("Q: integer1.equals(integer2) ?A:" + integer1.equals(integer2));   integer1 = new Integer(integer1);   integer2 = new Integer(integer2);   l.info("Q: integer1 == integer2 ?A:" + (integer1 == integer2));   l.info("Q: integer1.equals(integer2) ?A:" + integer1.equals(integer2));   Employee employee1 = new Employee();   Employee employee2 = new Employee();   l.info("Q: employee1 == employee2 ?A:" + (employee1 == employee2));   l.info("Q: employee1.equals(employee2) ?A :" + employee1.equals(employee2)); }

Sep 19, 2015 10:11:57 AM com.makotojava.intro.EmployeeTest anotherTest INFO:Q: integer1 == integer2 ?A: true Sep 19, 2015 10:11:57 AM com.makotojava.intro.EmployeeTest anotherTest INFO:Q: integer1.equals(integer2) ?A: true Sep 19, 2015 10:11:57 AM com.makotojava.intro.EmployeeTest anotherTest INFO:Q: integer1 == integer2 ?A: false Sep 19, 2015 10:11:57 AM com.makotojava.intro.EmployeeTest anotherTest INFO:Q: integer1.equals(integer2) ?A: true Sep 19, 2015 10:11:57 AM com.makotojava.intro.EmployeeTest anotherTest INFO:Q: employee1 == employee2 ?A: false Sep 19, 2015 10:11:57 AM com.makotojava.intro.EmployeeTest anotherTest INFO:Q: employee1.equals(employee2) ?A : false

@Override public boolean equals(Object obj) {   if (this == obj)     return true;   if (obj == null)     return false;   if (getClass() != obj.getClass())     return false;   Person other = (Person) obj;   if (age != other.age)     return false;   if (eyeColor == null) {     if (other.eyeColor != null)       return false;   } else if (!eyeColor.equals(other.eyeColor))     return false;   if (gender == null) {     if (other.gender != null)       return false;   } else if (!gender.equals(other.gender))     return false;   if (height != other.height)     return false;   if (name == null) {     if (other.name != null)       return false;   } else if (!name.equals(other.name))     return false;   if (weight != other.weight)     return false;   return true; }

@Test public void yetAnotherTest() {   Logger l = Logger.getLogger(Employee.class.getName());   Employee employee1 = new Employee();   employee1.setName("J Smith");   Employee employee2 = new Employee();   employee2.setName("J Smith");   l.info("Q: employee1 == employee2?      A:" + (employee1 == employee2));   l.info("Q: employee1.equals(employee2)?A:" + employee1.equals(employee2));     }

Sep 19, 2015 11:27:23 AM com.makotojava.intro.EmployeeTest yetAnotherTest INFO:Q: employee1 == employee2?      A: false Sep 19, 2015 11:27:23 AM com.makotojava.intro.EmployeeTest yetAnotherTest INFO:Q: employee1.equals(employee2)?A: true

@Override public String toString() {   return "Employee [taxpayerIdentificationNumber=" + taxpayerIdentificationNumber + ",        employeeNumber=" + employeeNumber + ", salary=" + salary + "]"; }

@Override public String toString() {   return super.toString() + "Employee [taxpayerIdentificationNumber=" + taxpayerIdentificationNumber +      ", employeeNumber=" + employeeNumber + ", salary=" + salary + "]"; }

@Override   public void printAudit(StringBuilder buffer) {   buffer.append(toString()); }

@Test public void yetAnotherTest() {   Logger l = Logger.getLogger(Employee.class.getName()); //    Employee employee1 = new Employee();   Employee employee1 = null;   employee1.setName("J Smith");   Employee employee2 = new Employee();   employee2.setName("J Smith");   l.info("Q: employee1 == employee2?      A:" + (employee1 == employee2));   l.info("Q: employee1.equals(employee2)?A:" + employee1.equals(employee2));     }

java.lang.NullPointerException   at com.makotojava.intro.EmployeeTest.yetAnotherTest(EmployeeTest.java:49)   .   .   .

IDE 警告

运行清单 10 的代码时可能会注意到，Eclipse 通过下面这条消息提醒潜在的错误： Null pointer access:The variable employee1 can only be null at this location.

Eclipse 会提醒许多潜在的开发错误 — 这是使用 IDE 执行 Java 开发的另一个优势。

@Test public void yetAnotherTest() {   Logger l = Logger.getLogger(Employee.class.getName());   //    Employee employee1 = new Employee();   try {     Employee employee1 = null;     employee1.setName("J Smith");     Employee employee2 = new Employee();     employee2.setName("J Smith");     l.info("Q: employee1 == employee2?      A:" + (employee1 == employee2));     l.info("Q: employee1.equals(employee2)?A:" + employee1.equals(employee2));   } catch (Exception e) {     l.severe("Caught exception:" + e.getMessage());   } finally {     // Always executes   } }

Sep 19, 2015 2:01:22 PM com.makotojava.intro.EmployeeTest yetAnotherTest SEVERE:Caught exception: null

@Test public void exceptionTest() {   Logger l = Logger.getLogger(Employee.class.getName());   File file = new File("file.txt");   BufferedReader bufferedReader = null;   try {     bufferedReader = new BufferedReader(new FileReader(file));     String line = bufferedReader.readLine();     while (line != null) {       // Read the file     }   } catch (FileNotFoundException e) {     l.severe(e.getMessage());   } catch (IOException e) {     l.severe(e.getMessage());   } catch (Exception e) {     l.severe(e.getMessage());   } finally {     // Close the reader   } }

@Test public void exceptionTestTryWithResources() {   Logger l = Logger.getLogger(Employee.class.getName());   File file = new File("file.txt");     try (BufferedReader bufferedReader = new BufferedReader(new FileReader(file))) {       String line = bufferedReader.readLine();       while (line != null) { // Read the file       }     } catch (Exception e) {       l.severe(e.getMessage());     } }

package com.makotojava.intro; public class HumanResourcesApplication {   public static void main(String[] args) {   } }

package com.makotojava.intro; import java.util.logging.Logger;  public class HumanResourcesApplication {   private static final Logger log = Logger.getLogger(HumanResourcesApplication.class.getName());   public static void main(String[] args) {     Employee e = new Employee();     e.setName("J Smith");     e.setEmployeeNumber("0001");     e.setTaxpayerIdentificationNumber("123-45-6789");     e.setSalary(BigDecimal.valueOf(45000.0));     e.printAudit(log);   } }

Sep 19, 2015 7:59:37 PM com.makotojava.intro.Person printAudit INFO:Name=J Smith,Age=0,Height=0,Weight=0,EyeColor=null,Gender=null/ TaxpayerIdentificationNumber=123-45-6789,EmployeeNumber=0001,Salary=45000.00

public class Person {      public static final String STATE_DELIMITER = "~";      public Person() {     // Default constructor   }      public enum Gender {     MALE,     FEMALE,     UNKNOWN   }      public Person(String name, int age, int height, int weight, String eyeColor, Gender gender) {     this.name = name;     this.age = age;     this.height = height;     this.weight = weight;     this.eyeColor = eyeColor;     this.gender = gender;   }    private String name;   private int age;   private int height;   private int weight;   private String eyeColor;   private Gender gender;

public class Employee extends Person {    private String taxpayerIdentificationNumber;   private String employeeNumber;   private BigDecimal salary;   // ... }

多重继承与单一继承

C++ 等语言支持多重继承 概念：在分层结构中的任一点，一个类都可继承一个或多个类。Java 语言仅支持单一继承— 意味着只能为一个类使用 extends 关键字。所以任何 Java 类的类分层结构始终包含一条一直到 java.lang.Object 的直线。但是，您在本教程后面会了解到，Java 语言支持在单个类中实现多个接口，因此为单一继承提供了一种规避方法。

public class Manager extends Employee {   // ... }

public class Person {   public Person() {   } }

public class Person { }

public class Person {   private String name;   public Person() {   }   public Person(String name) {     this.name = name;   } }  // Meanwhile, in Employee.java public class Employee extends Person {   public Employee() {     super("Elmer J Fudd");   } }

public class Person {   private String name;   public Person(String name) {     this.name = name;   } } // Meanwhile, in Employee.java public class Employee extends Person {   public Employee(String name) {     super(name);   } }

public class Person {   public Person() {   } } // Meanwhile, in Employee.java public class Employee extends Person {   public Employee() {   } }

public class Person {   public Person() {   } } // Meanwhile, in Employee.java public class Employee extends Person {   public Employee() {   super();   } }

public class Person {   private String name;   public Person(String name) {     this.name = name;   } } // Meanwhile, in Employee.java public class Employee extends Person {   public Employee() {   } }

public class Person {   private String name;   public Person() {     this("Some reasonable default?");   }   public Person(String name) {     this.name = name;   } }

public abstract class Employee extends Person {   // etc. }

public void someMethodSomwhere() {   Employee p = new Employee();// compile error!! }

public abstract class Employee extends Person {   public abstract boolean validate(); }

public class Executive extends Manager {   public Executive() {   } }

Manager m = new Manager(); Employee e = new Employee(); Person p = m; // okay p = e; // still okay Employee e2 = e; // yep, okay e = m; // still okay e2 = p; // wrong!

Manager m = new Manager(); Person p = m; // so far so good Employee e = m; // okay Employee e = p; // wrong!

public interfaceinterfaceName {     returnType methodName(argumentList);   }

public class Manager extends Employee implements BonusEligible, StockOptionRecipient {   // Etc... }

public interface BonusEligible { }

public interface StockOptionRecipient {   void processStockOptions(int numberOfOptions, BigDecimal price); }

public class className extends superclassName implements interfaceName {   // Class Body }

public class Manager extends Employee implements StockOptionRecipient {   public Manager() {   }   public void processStockOptions (int numberOfOptions, BigDecimal price) {     log.info("I can't believe I got " + number + " options at $" +     price.toPlainString() + "!");    } }

package com.makotojava.intro; import java.math.BigDecimal; import org.junit.Test; public class ManagerTest {   @Test   public void testCalculateAndAwardStockOptions() {     StockOptionEligible soe = new Manager();// perfectly valid     calculateAndAwardStockOptions(soe);     calculateAndAwardStockOptions(new Manager());// works too     }     public static void calculateAndAwardStockOptions(StockOptionEligible soe) {     BigDecimal reallyCheapPrice = BigDecimal.valueOf(0.01);     int numberOfOptions = 10000;     soe.awardStockOptions(numberOfOptions, reallyCheapPrice);   } }

 Manager m = new Manager();   StockOptionEligible soe = m; //okay   Employee e = soe; // Wrong!

public class EnclosingClass {   ...   public class NestedClass {   ...    } }

public class Manager extends Employee {   private DirectReports directReports;   public Manager() {   this.directReports = new DirectReports();   }   ...   private class DirectReports {   ...   } }

public class Manager extends Employee {   public Manager() {   }   ...   public class DirectReports {   ...   } } // public static void main(String[] args) {   Manager.DirectReports dr = new Manager.DirectReports();// This won't work! }

public class Manager extends Employee {   public Manager() {   }   ...   public class DirectReports {   ...   }   } // Meanwhile, in another method somewhere... public static void main(String[] args) {   Manager manager = new Manager();   Manager.DirectReports dr = manager.new DirectReports(); }

public class Manager extends Employee {   ...   public static class ManagerComparator implements Comparator<Manager> {   ...   }   } // Meanwhile, in another method somewhere... public static void main(String[] args) {   Manager.ManagerComparator mc = new Manager.ManagerComparator();   ... }

// From HumanResourcesApplication.java public void handleStockOptions(final Person person, StockOptionProcessingCallback callback) {   if (person instanceof StockOptionEligible) {     // Eligible Person, invoke the callback straight up     callback.process((StockOptionEligible)person);   } else if (person instanceof Employee) {     // Not eligible, but still an Employee.Let's cobble up a     /// anonymous inner class implementation for this     callback.process(new StockOptionEligible() {       @Override       public void awardStockOptions(int number, BigDecimal price) {         // This employee is not eligible         log.warning("It would be nice to award " + number + " of shares at $" +             price.setScale(2, RoundingMode.HALF_UP).toPlainString() +             ", but unfortunately, Employee " + person.getName() +              " is not eligible for Stock Options!");       }     });   } else {     callback.process(new StockOptionEligible() {       @Override       public void awardStockOptions(int number, BigDecimal price) {         log.severe("Cannot consider awarding " + number + " of shares at $" +             price.setScale(2, RoundingMode.HALF_UP).toPlainString() +             ", because " + person.getName() +              " does not even work here!");       }     });   } } // JUnit test to drive it (in HumanResourcesApplicationTest.java): @Test public void testHandleStockOptions() {   List<Person> people = HumanResourcesApplication.createPeople();   StockOptionProcessingCallback callback = new StockOptionProcessingCallback() {     @Override     public void process(StockOptionEligible stockOptionEligible) {       BigDecimal reallyCheapPrice = BigDecimal.valueOf(0.01);       int numberOfOptions = 10000;       stockOptionEligible.awardStockOptions(numberOfOptions, reallyCheapPrice);     }   };   for (Person person : people) {     classUnderTest.handleStockOptions(person, callback);   } }

Pattern pattern = Pattern.compile("a.*string");   Matcher matcher = pattern.matcher("a string");   boolean didMatch = matcher.matches();   Logger.getAnonymousLogger().info (didMatch);   int patternStartIndex = matcher.start();   Logger.getAnonymousLogger().info (patternStartIndex);   int patternEndIndex = matcher.end();   Logger.getAnonymousLogger().info (patternEndIndex);

Here is a string with more than just the pattern.

MyWikiWord

Here is a WikiWord followed by AnotherWikiWord, then YetAnotherWikiWord.

[A-Z][a-z]*([A-Z][a-z]*)+

String input = "Here is a WikiWord followed by AnotherWikiWord, then SomeWikiWord."; Pattern pattern = Pattern.compile("[A-Z][a-z]*([A-Z][a-z]*)+"); Matcher matcher = pattern.matcher(input); while (matcher.find()) {   Logger.getAnonymousLogger().info("Found this wiki word:" + matcher.group()); }

String input = "Here is a WikiWord followed by AnotherWikiWord, then SomeWikiWord."; Pattern pattern = Pattern.compile("[A-Z][a-z]*([A-Z][a-z]*)+"); Matcher matcher = pattern.matcher(input); Logger.getAnonymousLogger().info("Before:" + input); String result = matcher.replaceAll("replacement"); Logger.getAnonymousLogger().info("After:" + result);

Before:Here is WikiWord followed by AnotherWikiWord, then SomeWikiWord.   After:Here is replacement followed by replacement, then replacement.

Before:Here is a WikiWord followed by AnotherWikiWord, then SomeWikiWord.   After:Here is a replacement followed by AnotherWikiWord, then SomeWikiWord.

String input = "Here is a WikiWord followed by AnotherWikiWord, then SomeWikiWord."; Pattern pattern = Pattern.compile("[A-Z][a-z]*([A-Z][a-z]*)+"); Matcher matcher = pattern.matcher(input); Logger.getAnonymousLogger().info("Before:" + input); String result = matcher.replaceAll("blah$0blah"); Logger.getAnonymousLogger().info("After:" + result);

Before:Here is a WikiWord followed by AnotherWikiWord, then SomeWikiWord.   After:Here is a blahWikiWordblah followed by blahAnotherWikiWordblah,   then blahSomeWikiWordblah.

StringBuffer buffer = new StringBuffer(); while (matcher.find()) {   matcher.appendReplacement(buffer, "blah$0blah"); } matcher.appendTail(buffer); Logger.getAnonymousLogger().info("After:" + buffer.toString());

Before:Here is a WikiWord followed by AnotherWikiWord, then SomeWikiWord.   After:Here is a blahWikiWordblah followed by blahAnotherWikiWordblah,   then blahSomeWikiWordblah.

ArrayList arrayList = new ArrayList(); arrayList.add("A String"); arrayList.add(new Integer(10)); arrayList.add("Another String"); // So far, so good.

ArrayList arrayList = new ArrayList(); arrayList.add("A String"); arrayList.add(new Integer(10)); arrayList.add("Another String"); // So far, so good. *processArrayList(arrayList); *// In some later part of the code... private void processArrayList(ArrayList theList) {   for (int aa = 0; aa < theList.size(); aa++) {     // At some point, this will fail...     String s = (String)theList.get(aa);   } }

ArrayList<String> arrayList = new ArrayList<>(); arrayList.add("A String"); arrayList.add(new Integer(10));// compiler error! arrayList.add("Another String"); // So far, so good. *processArrayList(arrayList); *// In some later part of the code... private void processArrayList(ArrayList<String> theList) {   for (int aa = 0; aa < theList.size(); aa++) {     // No cast necessary...     String s = theList.get(aa);   } }

private void processArrayList(ArrayList<String> theList) {   for (String s : theList) {     String s = theList.get(aa);   } }

List<E> listReference = new concreteListClass<E>();

List<Integer> listOfIntegers = new ArrayList<Integer>();

package com.makotojava.intro; import java.util.ArrayList; import java.util.List; public class SimpleList<E> {   private List<E> backingStore;   public SimpleList() {     backingStore = new ArrayList<E>();   }   public E add(E e) {     if (backingStore.add(e))     return e;     else     return null;   }   public int size() {     return backingStore.size();   }   public void clear() {     backingStore.clear();   } }

package com.makotojava.intro; import java.math.BigDecimal; import java.util.logging.Logger; import org.junit.Test; public class SimpleListTest {   @Test   public void testAdd() {     Logger log = Logger.getLogger(SimpleListTest.class.getName());          SimpleList<BigDecimal> sl = new SimpleList<>();     sl.add(BigDecimal.ONE);     log.info("SimpleList size is :" + sl.size());     sl.add(BigDecimal.ZERO);     log.info("SimpleList size is :" + sl.size());     sl.clear();     log.info("SimpleList size is :" + sl.size());   } }

Sep 20, 2015 10:24:33 AM com.makotojava.intro.SimpleListTest testAdd  INFO:SimpleList size is:1 Sep 20, 2015 10:24:33 AM com.makotojava.intro.SimpleListTest testAdd  INFO:SimpleList size is:2 Sep 20,  2015 10:24:33 AM com.makotojava.intro.SimpleListTest testAdd  INFO:SimpleList size is:0

public class Person {   public static final String MALE = "male";   public static final String FEMALE = "female"; }

public void myMethod() {   //...   String genderMale = Person.MALE;   //... }

public enum Gender {   MALE,   FEMALE }

package com.makotojava.intro;  public enum Gender {   MALE("male"),   FEMALE("female");    private String displayName;   private Gender(String displayName) {     this.displayName = displayName;   }    public String getDisplayName() {     return this.displayName;   } }

package com.makotojava.intro; public interface Displayable {   public String getDisplayName(); }

package com.makotojava.intro;  public enum Gender implements Displayable {   MALE("male"),   FEMALE("female");    private String displayName;   private Gender(String displayName) {     this.displayName = displayName;   }   @Override   public String getDisplayName() {     return this.displayName;   } }

File f = new File("temp.txt"); File f2 = new File("/home/steve/testFile.txt");

File f2 = new File("/home/steve/testFile.txt"); if (f2.exists()) {   // File exists.Process it... } else {   // File doesn't exist.Create it...   f2.createNewFile(); }

public List<Employee> readFromDisk(String filename) {   final String METHOD_NAME = "readFromDisk(String filename)";   List<Employee> ret = new ArrayList<>();   File file = new File(filename);   try (InputStreamReader reader = new InputStreamReader(new FileInputStream(file))) {     StringBuilder sb = new StringBuilder();     int numberOfEmployees = 0;     int character = reader.read();     while (character != -1) {         sb.append((char)character);         character = reader.read();     }     log.info("Read file:/n" + sb.toString());     int index = 0;     while (index < sb.length()-1) {       StringBuilder line = new StringBuilder();       while ((char)sb.charAt(index) != '/n') {         line.append(sb.charAt(index++));       }       StringTokenizer strtok = new StringTokenizer(line.toString(), Person.STATE_DELIMITER);       Employee employee = new Employee();       employee.setState(strtok);       log.info("Read Employee:" + employee.toString());       ret.add(employee);       numberOfEmployees++;       index++;     }     log.info("Read " + numberOfEmployees + " employees from disk.");   } catch (FileNotFoundException e) {     log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "Cannot find file " +         file.getName() + ", message = " + e.getLocalizedMessage(), e);   } catch (IOException e) {     log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "IOException occurred,         message = " + e.getLocalizedMessage(), e);   }   return ret; }

public boolean saveToDisk(String filename, List<Employee> employees) {   final String METHOD_NAME = "saveToDisk(String filename, List<Employee> employees)";      boolean ret = false;   File file = new File(filename);   try (OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(file))) {     log.info("Writing " + employees.size() + " employees to disk (as String)...");     for (Employee employee : employees) {       writer.write(employee.getState()+"/n");     }     ret = true;     log.info("Done.");   } catch (FileNotFoundException e) {     log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "Cannot find file " +         file.getName() + ", message = " + e.getLocalizedMessage(), e);   } catch (IOException e) {     log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "IOException occurred,         message = " + e.getLocalizedMessage(), e);   }   return ret; }

public List<Employee> readFromDiskBuffered(String filename) {   final String METHOD_NAME = "readFromDisk(String filename)";   List<Employee> ret = new ArrayList<>();   File file = new File(filename);   try (BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(file)))) {     String line = reader.readLine();     int numberOfEmployees = 0;     while (line != null) {       StringTokenizer strtok = new StringTokenizer(line, Person.STATE_DELIMITER);       Employee employee = new Employee();       employee.setState(strtok);       log.info("Read Employee:" + employee.toString());       ret.add(employee);       numberOfEmployees++;       // Read next line       line = reader.readLine();     }     log.info("Read " + numberOfEmployees + " employees from disk.");   } catch (FileNotFoundException e) {     log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "Cannot find file " +         file.getName() + ", message = " + e.getLocalizedMessage(), e);   } catch (IOException e) {     log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "IOException occurred,         message = " + e.getLocalizedMessage(), e);   }   return ret; }

public boolean saveToDiskBuffered(String filename, List<Employee> employees) {   final String METHOD_NAME = "saveToDisk(String filename, List<Employee> employees)";      boolean ret = false;   File file = new File(filename);   try (BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file)))) {     log.info("Writing " + employees.size() + " employees to disk (as String)...");     for (Employee employee : employees) {       writer.write(employee.getState()+"/n");     }     ret = true;     log.info("Done.");   } catch (FileNotFoundException e) {     log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "Cannot find file " +         file.getName() + ", message = " + e.getLocalizedMessage(), e);   } catch (IOException e) {     log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "IOException occurred,         message = " + e.getLocalizedMessage(), e);   }   return ret; }

import java.io.Serializable; public class Person implements Serializable {   // etc... }

public class HumanResourcesApplication {   private static final Logger log = Logger.getLogger(HumanResourcesApplication.class.getName());   private static final String SOURCE_CLASS = HumanResourcesApplication.class.getName();      public static List<Employee> createEmployees() {     List<Employee> ret = new ArrayList<Employee>();     Employee e = new Employee("Jon Smith", 45, 175, 75, "BLUE", Gender.MALE,         "123-45-9999", "0001", BigDecimal.valueOf(100000.0));     ret.add(e);     //     e = new Employee("Jon Jones", 40, 185, 85, "BROWN", Gender.MALE, "223-45-9999",         "0002", BigDecimal.valueOf(110000.0));     ret.add(e);     //     e = new Employee("Mary Smith", 35, 155, 55, "GREEN", Gender.FEMALE, "323-45-9999",         "0003", BigDecimal.valueOf(120000.0));     ret.add(e);     //     e = new Employee("Chris Johnson", 38, 165, 65, "HAZEL", Gender.UNKNOWN,         "423-45-9999", "0004", BigDecimal.valueOf(90000.0));     ret.add(e);     // Return list of Employees     return ret;   }      public boolean serializeToDisk(String filename, List<Employee> employees) {     final String METHOD_NAME = "serializeToDisk(String filename, List<Employee> employees)";          boolean ret = false;// default: failed     File file = new File(filename);     try (ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream(file))) {       log.info("Writing " + employees.size() + " employees to disk (using Serializable)...");       outputStream.writeObject(employees);       ret = true;       log.info("Done.");     } catch (IOException e) {       log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "Cannot find file " +         file.getName() + ", message = " + e.getLocalizedMessage(), e);     }     return ret;   }

public class HumanResourcesApplicationTest {    private HumanResourcesApplication classUnderTest;   private List<Employee> testData;      @Before   public void setUp() {     classUnderTest = new HumanResourcesApplication();     testData = HumanResourcesApplication.createEmployees();   }   @Test   public void testSerializeToDisk() {     String filename = "employees-Junit-" + System.currentTimeMillis() + ".ser";     boolean status = classUnderTest.serializeToDisk(filename, testData);     assertTrue(status);   } }

public class HumanResourcesApplication {    private static final Logger log = Logger.getLogger(HumanResourcesApplication.class.getName());   private static final String SOURCE_CLASS = HumanResourcesApplication.class.getName();      @SuppressWarnings("unchecked")   public List<Employee> deserializeFromDisk(String filename) {     final String METHOD_NAME = "deserializeFromDisk(String filename)";          List<Employee> ret = new ArrayList<>();     File file = new File(filename);     int numberOfEmployees = 0;     try (ObjectInputStream inputStream = new ObjectInputStream(new FileInputStream(file))) {       List<Employee> employees = (List<Employee>)inputStream.readObject();       log.info("Deserialized List says it contains " + employees.size() +           " objects...");       for (Employee employee : employees) {         log.info("Read Employee:" + employee.toString());         numberOfEmployees++;       }       ret = employees;       log.info("Read " + numberOfEmployees + " employees from disk.");     } catch (FileNotFoundException e) {       log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "Cannot find file " +           file.getName() + ", message = " + e.getLocalizedMessage(), e);     } catch (IOException e) {       log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "IOException occurred,         message = " + e.getLocalizedMessage(), e);     } catch (ClassNotFoundException e) {       log.logp(Level.SEVERE, SOURCE_CLASS, METHOD_NAME, "ClassNotFoundException,           message = " + e.getLocalizedMessage(), e);     }     return ret;   }    }

public class HumanResourcesApplicationTest {      private HumanResourcesApplication classUnderTest;      private List<Employee> testData;      @Before   public void setUp() {     classUnderTest = new HumanResourcesApplication();   }      @Test   public void testDeserializeFromDisk() {     String filename = "employees-Junit-" + System.currentTimeMillis() + ".ser";     int expectedNumberOfObjects = testData.size();     classUnderTest.serializeToDisk(filename, testData);     List<Employee> employees = classUnderTest.deserializeFromDisk(filename);     assertEquals(expectedNumberOfObjects, employees.size());   }  }

import java.io.Serializable;   public class Person implements Serializable {   private static final long serialVersionUID = 20100515;   // etc...   }