Java自学笔记03—对象与类（上） - 黑马程序员技术交流社区

import java.text.DateFormatSymbols;
import java.util.*;
public class HelloJava
{
public static void main(String[] args)
{
GregorianCalendar d = new GregorianCalendar();
int today = d.get(Calendar.DAY_OF_MONTH);
int month = d.get(Calendar.MONTH);
d.set(Calendar.DAY_OF_MONTH, 1);
int weekday = d.get(Calendar.DAY_OF_WEEK);
int firstDayOfWeek = d.getFirstDayOfWeek();
int indent = 0;
while (weekday != firstDayOfWeek)
{
indent++;
d.add(Calendar.DAY_OF_MONTH, -1);
weekday = d.get(Calendar.DAY_OF_WEEK);
}
String[] weekdayNames = new DateFormatSymbols().getShortWeekdays();
do
{
System.out.printf("%4s", weekdayNames[weekday]);
d.add(Calendar.DAY_OF_MONTH, 1);
weekday = d.get(Calendar.DAY_OF_WEEK);
}
while (weekday != firstDayOfWeek);
System.out.println();
for (int i = 1; i <= indent; i++)
System.out.print(" ");
d.set(Calendar.DAY_OF_MONTH, 1);
do
{
int day = d.get(Calendar.DAY_OF_MONTH);
System.out.printf("%3d", day);
if (day == today)
System.out.print("*");
else
System.out.print(" ");
d.add(Calendar.DAY_OF_MONTH, 1);
weekday = d.get(Calendar.DAY_OF_WEEK);
if (weekday == firstDayOfWeek)
System.out.println();
}
while (d.get(Calendar.MONTH) == month);
if (weekday != firstDayOfWeek)
System.out.println();
}
}

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用户自定义类
class ClassName
{
field1
field2
…
constructor1
constructor2
…
method1
method2
…
}

import java.util.*;
public class HelloJava
{
public static void main(String[] args)
{
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);
for (Employee e : staff)
e.raiseSalary(5);
for (Employee e : staff)
System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay=" + e.getHireDay());
}
}
class Employee
{
private String name;
private double salary;
private Date hireDay;
public Employee(String n, double s, int year, int month, int day)
{
name = n;
salary = s;
GregorianCalendar calendar = new GregorianCalendar(year, month - 1, day);
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;
}
}

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静态域与静态方法
静态域可以将类中的域分为静态域和实例域。
实例域是指本类所有对象都各自拥有的域。
静态域是指本类所有对象都共享的域。
实例域属于对象，存储在堆中。
静态域属于类，存储在静态存储区中。
只要类已经载入内存，即使还没有创建对象，静态域也已经存在了。
静态方法可以将类中的方法分为实例方法和静态方法。
调用实例方法，须用对象.实例方法的形式，调用时，将在栈内存中开辟空间。
调用静态方法，可用类名.静态方法的形式，静态方法随着类的加载已经存在于静态存储区，不会在调用时开辟内存。
静态方法可以访问本类的静态域，但不能访问本类对象的实力域。
main方法每一个类可以有一个main方法，这个特性常用于对类进行单元测试。

public class HelloJava
{
public static void main(String[] args)
{
Employee[] staff = new Employee[3];
staff[0] = new Employee("Tom", 40000);
staff[1] = new Employee("Dick", 60000);
staff[2] = new Employee("Harry", 65000);
for (Employee e : staff)
{
e.setId();
System.out.println("name=" + e.getName() + ",id=" + e.getId() + ",salary=" + e.getSalary());
}
int n = Employee.getNextId();
System.out.println("Next available id=" + n);
}
}
class Employee
{
private static int nextId = 1;
private String name;
private double salary;
private int id;
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;
nextId++;
}
public static int getNextId()
{
return nextId;
}
public static void main(String[] args)
{
Employee e = new Employee("Harry", 50000);
System.out.println(e.getName() + " " + e.getSalary());
}
}

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