本文目录一览：
- 1、在Java中具体讲解什么叫做类
- 2、Java类的定义
- 3、java 定义类 如何写？
在Java中具体讲解什么叫做类
嗨 你好啊
类可解为以下：
类（Class）实际上是对某种类型的对象定义变量和方法的原型。它表示对现实生活中一类具有共同特征的事物的抽象，是面向对象编程的基础。
类是对某个对象的定义。它包含有关对象动作方式的信息，包括它的名称、方法、属性和事件。实际上它本身并不是对象，因为它不存在于内存中。当引用类的代码运行时，类的一个新的实例，即对象，就在内存中创建了。虽然只有一个类，但能从这个类在内存中创建多个相同类型的对象。类通过接口与外界发生关系。
可以把类看作“理论上”的对象，也就是说，它为对象提供蓝图，但在内存中并不存在。从这个蓝图可以创建任何数量的对象。从类创建的所有对象都有相同的成员：属性、方法和事件。但是，每个对象都象一个独立的实体一样动作。例如，一个对象的属性可以设置成与同类型的其他对象不同的值。
希望可以给你在学习Java的路上带来力所能及的帮助
Java类的定义
package java.lancs ;
/**
* Graphics objects for practical classes (Java 1.1 version)
* @author Roger Garside/Richard Cardoe
* @version Last Rewritten: 24/Sept/97
*/
import java.awt.* ;
import java.awt.event.* ;
/*
* class to hold details about the shape to draw
*/
class BasicShape
{
// name of the shape - RECTANGLE, OVAL, etc.
int shape ;
// dimensions of the shape
int x, y, w, h ;
// colour of the shape
Color colour ;
// constructor to initialise the variables to default values
public BasicShape()
{
shape = -1 ;
x = -1 ;
y = -1 ;
w = -1 ;
h = -1 ;
colour = Color.green ;
} // end of constructor method
// constructor to initialise the variables to specifier values
public BasicShape(int sh, int x1, int y1, int w1, int h1, Color col)
{
shape = sh ;
x = x1 ;
y = y1 ;
w = w1 ;
h = h1 ;
colour = col ;
} // end of constructor method
} // end of class BasicShape
/*
* a canvas to draw on
*/
class BasicCanvas extends Canvas
{
BasicGraphics parent ;
// constructor method
public BasicCanvas(BasicGraphics p)
{
parent = p ;
} // end of constructor method
// called when class is initialised to put window on the screen
// or when window needs to be redrawn
public void paint(Graphics g)
{
Dimension d = getSize() ;
int cx = d.width / 2,
cy = d.height /2 ;
g.setColor(Color.black) ;
g.drawRect(1, 1, d.width - 3, d.height - 3) ;
int yy = 25 ;
while (yy d.height)
{
if (yy % 100 == 0)
{
g.drawLine(1, yy, 11, yy) ;
g.drawLine(d.width - 13, yy, d.width - 3, yy) ;
}
else
{
g.drawLine(1, yy, 6, yy) ;
g.drawLine(d.width - 8, yy, d.width - 3, yy) ;
}
yy += 25 ;
}
int xx = 25 ;
while (xx d.width)
{
if (xx % 100 == 0)
{
g.drawLine(xx, 1, xx, 11) ;
g.drawLine(xx, d.height - 13, xx, d.height - 3) ;
}
else
{
g.drawLine(xx, 1, xx, 6) ;
g.drawLine(xx, d.height - 8, xx, d.height - 3) ;
}
xx += 25 ;
}
for (int i = 0 ; i parent.noOfShapes ; i++)
{
g.setColor(parent.shapeList[i].colour) ;
if (parent.shapeList[i].shape == BasicGraphics.RECTANGLE)
{
g.drawRect(parent.shapeList[i].x, parent.shapeList[i].y,
parent.shapeList[i].w, parent.shapeList[i].h) ;
}
else if (parent.shapeList[i].shape == BasicGraphics.FILLED_RECTANGLE)
{
g.fillRect(parent.shapeList[i].x, parent.shapeList[i].y,
parent.shapeList[i].w, parent.shapeList[i].h) ;
}
else if (parent.shapeList[i].shape == BasicGraphics.OVAL)
{
g.drawOval(parent.shapeList[i].x, parent.shapeList[i].y,
parent.shapeList[i].w, parent.shapeList[i].h) ;
}
else if (parent.shapeList[i].shape == BasicGraphics.FILLED_OVAL)
{
g.fillOval(parent.shapeList[i].x, parent.shapeList[i].y,
parent.shapeList[i].w, parent.shapeList[i].h) ;
}
else if ((parent.shapeList[i].shape == BasicGraphics.TRIANGLE) ||
(parent.shapeList[i].shape == BasicGraphics.FILLED_TRIANGLE))
{
int x1 = parent.shapeList[i].x ;
int y1 = parent.shapeList[i].y ;
int w1 = parent.shapeList[i].w ;
int h1 = parent.shapeList[i].h ;
Polygon p = new Polygon() ;
p.addPoint(x1, y1 + h1) ;
p.addPoint(x1 + w1, y1 + h1) ;
p.addPoint(x1 + (w1 / 2), y1) ;
p.addPoint(x1, y1 + h1) ;
if (parent.shapeList[i].shape == BasicGraphics.TRIANGLE)
g.drawPolygon(p) ;
else
g.fillPolygon(p) ;
}
}
} // end of method paint
} // end of class BasicCanvas
/*
* class to draw simple shapes in a window
*/
public class BasicGraphics extends Frame implements ActionListener
{
// maximum width of window
private static final int MAX_WIDTH = 600 ;
// maximum height of window
private static final int MAX_HEIGHT = 400 ;
/**
* definition of a rectangle shape
*/
public static final int RECTANGLE = 1 ;
/**
* definition of an oval shape
*/
public static final int OVAL = 2 ;
/**
* definition of a triangle shape
*/
public static final int TRIANGLE = 3 ;
/**
* definition of a filled-in rectangle
*/
public static final int FILLED_RECTANGLE = 4 ;
/**
* definition of a filled-in oval
*/
public static final int FILLED_OVAL = 5 ;
/**
* definition of a filled-in triangle
*/
public static final int FILLED_TRIANGLE = 6 ;
BasicShape[] shapeList = new BasicShape[50];
int noOfShapes = 0;
private BasicShape newShape = new BasicShape();
private Button quit ;
/**
* constructor to lay out the window
*/
public BasicGraphics()
{
setTitle("BasicGraphics Window") ;
setSize(MAX_WIDTH, MAX_HEIGHT + 50) ;
BasicCanvas c = new BasicCanvas(this) ;
add("Center", c) ;
Panel p = new Panel() ;
p.setLayout(new FlowLayout()) ;
quit = new Button("Quit") ;
p.add(quit) ;
quit.addActionListener(this) ;
add("South", p) ;
} // end of constructor method
/**
* handles button depression events, etc.
*/
public void actionPerformed(ActionEvent event)
{
dispose() ;
System.exit(0) ;
} // end of method actionPerformed
/**
* set the type of shape that you want to draw
* @param shape e.g. BasicGraphics.RECTANGLE
*/
public void setShape(int shape)
{
if ((shape != RECTANGLE) (shape != FILLED_RECTANGLE)
(shape != OVAL) (shape != FILLED_OVAL)
(shape != TRIANGLE) (shape != FILLED_TRIANGLE))
{
System.err.println("This is not a valid shape");
System.exit(1);
}
newShape.shape = shape ;
} // end of method setShape
/**
* set the dimensions of the shape that you want to draw
* @param x x-coordinate of the top left hand corner of the bounding
* rectangle
* @param y y-coordinate of the top left hand corner of the bounding
* rectangle
* @param w width of the bounding rectangle
* @param h height of the bounding rectangle
*/
public void setDimensions(int x, int y, int w, int h)
{
if (newShape.shape == -1)
{
System.err.println("You need to set the shape first");
System.exit(1);
}
if ((x 5) || (y 5) || (w 5) || (h 5) ||
(x + w MAX_WIDTH - 5) || (y + h MAX_HEIGHT - 5))
{
System.err.println("Invalid dimensions supplied") ;
System.exit(1);
}
newShape.x = x ;
newShape.y = y ;
newShape.w = w ;
newShape.h = h ;
} // end of method setDimensions
/**
* set the colour of the shape that you want to draw
* @param colour the Color type (Color.red, Color.blue, etc.)
*/
public void setColour(Color colour)
{
if (newShape.x == -1)
{
System.err.println("You need to set the dimensions first");
System.exit(1);
}
newShape.colour = colour ;
shapeList[noOfShapes] = new BasicShape(newShape.shape,
newShape.x, newShape.y,
newShape.w, newShape.h,
newShape.colour) ;
noOfShapes++ ;
newShape = new BasicShape() ;
} // end of method setColour
/**
* draws the window on the screen with the specified shapes
*/
public void draw()
{
setVisible(true) ;
} // end of method draw
} // end of class BasicGraphics
java 定义类 如何写？
类是一种引用数据类型。类为对象的模板，简单的说就是分类。
类的定义包括“成员变量”的定义和“方法”的定义，其中“成员变量”用于描述一类对象共同的数据结构。在Java语言中，类的成员变量的定义可以使用如下语法：
class 类名 {
成员变量类型变量名称；
………
}
类是用class关键字来定义的一种抽象数据类型，类不但定义了抽象数据类型的组成（成员变量），同时还定义了对该类型可以实施的操作（方法），类名的首字母必须大写。看如下代码定义了雇员类:
/** 定义雇员类 */
public class Emp{
String name;
int age;
char gender;
double salary;
}
在如上的实例代码中，仅仅定义了Emp类型的组成，即成员变量。该类定义了4个成员变量：String类型的name用于存放名字；int类型的age用于存放年龄；char类型的gender用于存放性别；double类型的salary用于存放工资。
