corejava[读书笔记]第四章-优快云博客

本文链接：https://blog.youkuaiyun.com/BaiShuHeiYing/article/details/9455741

本文通过多个示例展示了Java中如何创建并使用员工类，包括设置薪资、提高薪资百分比、静态方法的应用、参数传递特性及构造函数的多种实现方式。

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例4-2

import java.util.*;

/**
 * This program tests the Employee class.
 * @version 1.11 2004-02-19
 * @author Cay Horstmann
 */
public class EmployeeTest
{
   public static void main(String[] args)
   {
      // fill the staff array with three Employee objects
      Employee[] staff = new Employee[3];

      staff[0] = new Employee("Carl Cracker", 75000, 1987, 12, 15);
      staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
      staff[2] = new Employee("Tony Tester", 40000, 1990, 3, 15);

      // raise everyone's salary by 5%
      for (Employee e : staff)
         e.raiseSalary(5);

      // print out information about all Employee objects
      for (Employee e : staff)
         System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
               + e.getHireDay());
   }
}

class Employee
{
   public Employee(String n, double s, int year, int month, int day)
   {
      name = n;
      salary = s;
      
      //month-1 为什么？
      GregorianCalendar calendar = new GregorianCalendar(year, month - 1, day);
      // GregorianCalendar uses 0 for January
      hireDay = calendar.getTime();
   }

   public String getName()
   {
      return name;
   }

   public double getSalary()
   {
      return salary;
   }

   public Date getHireDay()
   {
      return hireDay;
   }

   public void raiseSalary(double byPercent)
   {
      double raise = salary * byPercent / 100;
      salary += raise;
   }

   private String name;
   private double salary;
   private Date hireDay;
}

执行结果：

name=Carl Cracker,salary=78750.0,hireDay=Tue Dec 15 00:00:00 CST 1987
name=Harry Hacker,salary=52500.0,hireDay=Sun Oct 01 00:00:00 CST 1989
name=Tony Tester,salary=42000.0,hireDay=Thu Mar 15 00:00:00 CST 1990

例4-3

package com.itquanta;
/**
 * This program demonstrates static methods.
 * @version 1.01 2004-02-19
 * @author Cay Horstmann
 */
public class StaticTest
{
   public static void main(String[] args)
   {
      // fill the staff array with three Employee objects
      Employee[] staff = new Employee[3];

      staff[0] = new Employee("Tom", 40000);
      staff[1] = new Employee("Dick", 60000);
      staff[2] = new Employee("Harry", 65000);

      // print out information about all Employee objects
      for (Employee e : staff)
      {
         e.setId();
         System.out.println("name=" + e.getName() + ",id=" + e.getId() + ",salary="
               + e.getSalary());
      }

      int n = Employee.getNextId(); // calls static method
      System.out.println("Next available id=" + n);
   }
}

class Employee
{
   public Employee(String n, double s)
   {
      name = n;
      salary = s;
      id = 0;
   }

   public String getName()
   {
      return name;
   }

   public double getSalary()
   {
      return salary;
   }

   public int getId()
   {
      return id;
   }

   public void setId()
   {
      id = nextId; // set id to next available id
      nextId++;
   }

   public static int getNextId()
   {
      return nextId; // returns static field
   }

   public static void main(String[] args) // unit test
   {
      Employee e = new Employee("Harry", 50000);
      System.out.println(e.getName() + " " + e.getSalary());
   }

   private String name;
   private double salary;
   private int id;
   private static int nextId = 1;
}

执行结果：

name=Tom,id=1,salary=40000.0
name=Dick,id=2,salary=60000.0
name=Harry,id=3,salary=65000.0
Next available id=4

例4-4

package com.itquanta;
/**
 * This program demonstrates parameter passing in Java.
 * @version 1.00 2000-01-27
 * @author Cay Horstmann
 */
public class ParamTest
{
   public static void main(String[] args)
   {
      /*
       * Test 1: Methods can't modify numeric parameters
       */
      System.out.println("Testing tripleValue:");
      double percent = 10;
      System.out.println("Before: percent=" + percent);
      tripleValue(percent);
      System.out.println("After: percent=" + percent);

      /*
       * Test 2: Methods can change the state of object parameters
       */
      System.out.println("\nTesting tripleSalary:");
      Employee harry = new Employee("Harry", 50000);
      System.out.println("Before: salary=" + harry.getSalary());
      tripleSalary(harry);
      System.out.println("After: salary=" + harry.getSalary());

      /*
       * Test 3: Methods can't attach new objects to object parameters
       */
      System.out.println("\nTesting swap:");
      Employee a = new Employee("Alice", 70000);
      Employee b = new Employee("Bob", 60000);
      System.out.println("Before: a=" + a.getName());
      System.out.println("Before: b=" + b.getName());
      swap(a, b);
      System.out.println("After: a=" + a.getName());
      System.out.println("After: b=" + b.getName());
   }

   public static void tripleValue(double x) // doesn't work
   {
      x = 3 * x;
      System.out.println("End of method: x=" + x);
   }

   public static void tripleSalary(Employee x) // works
   {
      x.raiseSalary(200);
      System.out.println("End of method: salary=" + x.getSalary());
   }

   public static void swap(Employee x, Employee y)
   {
      Employee temp = x;
      x = y;
      y = temp;
      System.out.println("End of method: x=" + x.getName());
      System.out.println("End of method: y=" + y.getName());
   }
}

class Employee // simplified Employee class
{
   public Employee(String n, double s)
   {
      name = n;
      salary = s;
   }

   public String getName()
   {
      return name;
   }

   public double getSalary()
   {
      return salary;
   }

   public void raiseSalary(double byPercent)
   {
      double raise = salary * byPercent / 100;
      salary += raise;
   }

   private String name;
   private double salary;
}

执行结果：

Testing tripleValue:
Before: percent=10.0
End of method: x=30.0
After: percent=10.0

Testing tripleSalary:
Before: salary=50000.0
End of method: salary=150000.0
After: salary=150000.0

Testing swap:
Before: a=Alice
Before: b=Bob
End of method: x=Bob
End of method: y=Alice
After: a=Alice
After: b=Bob

例4-5

package com.itquanta;

import java.util.Random;

/**
 * This program demonstrates object construction.
 * 
 * @version 1.01 2004-02-19
 * @author Cay Horstmann
 */
public class ConstructorTest {
	public static void main(String[] args) {
		// fill the staff array with three Employee objects
		Employee[] staff = new Employee[3];

		staff[0] = new Employee("Harry", 40000);
		staff[1] = new Employee(60000);
		staff[2] = new Employee();

		// print out information about all Employee objects
		for (Employee e : staff)
			System.out.println("name=" + e.getName() + ",id=" + e.getId()
					+ ",salary=" + e.getSalary());
	}
}

class Employee {
	// three overloaded constructors
	public Employee(String n, double s) {
		name = n;
		salary = s;
	}

	public Employee(double s) {
		// calls the Employee(String, double) constructor
		this("Employee #" + nextId, s);
	}

	// the default constructor
	public Employee() {
		// name initialized to ""--see below
		// salary not explicitly set--initialized to 0
		// id initialized in initialization block
	}

	public String getName() {
		return name;
	}

	public double getSalary() {
		return salary;
	}

	public int getId() {
		return id;
	}

	private static int nextId;

	private int id;
	private String name = ""; // instance field initialization
	private double salary;

	// static initialization block
	static {
		Random generator = new Random();
		// set nextId to a random number between 0 and 9999
		nextId = generator.nextInt(10000);
	}

	// object initialization block
	{
		id = nextId;
		nextId++;
	}
}

运行结果：

name=Harry,id=8638,salary=40000.0
name=Employee #8639,id=8639,salary=60000.0
name=,id=8640,salary=0.0

例4-6

package com.itquanta;
import com.horstmann.corejava.Employee;
// the Employee class is defined in that package

import static java.lang.System.*;

/**
 * This program demonstrates the use of packages.
 * @author cay
 * @version 1.11 2004-02-19
 * @author Cay Horstmann
 */
public class PackageTest
{
   public static void main(String[] args)
   {
      // because of the import statement, we don't have to use com.horstmann.corejava.Employee here
      Employee harry = new Employee("Harry Hacker", 50000, 1989, 10, 1);

      harry.raiseSalary(5);

      // because of the static import statement, we don't have to use System.out here
      out.println("name=" + harry.getName() + ",salary=" + harry.getSalary());
   }
}

例4-7

package com.horstmann.corejava;

// the classes in this file are part of this package

import java.util.*;

// import statements come after the package statement

/**
 * @version 1.10 1999-12-18
 * @author Cay Horstmann
 */
public class Employee
{
   public Employee(String n, double s, int year, int month, int day)
   {
      name = n;
      salary = s;
      GregorianCalendar calendar = new GregorianCalendar(year, month - 1, day);
      // GregorianCalendar uses 0 for January
      hireDay = calendar.getTime();
   }

   public String getName()
   {
      return name;
   }

   public double getSalary()
   {
      return salary;
   }

   public Date getHireDay()
   {
      return hireDay;
   }

   public void raiseSalary(double byPercent)
   {
      double raise = salary * byPercent / 100;
      salary += raise;
   }

   private String name;
   private double salary;
   private Date hireDay;
}

执行结果：

name=Harry Hacker,salary=52500.0

第四章所有代码完。