本文目錄一覽：
在Java中具體講解什麼叫做類
嗨 你好啊
類可解為以下：
類（Class）實際上是對某種類型的對象定義變數和方法的原型。它表示對現實生活中一類具有共同特徵的事物的抽象，是面向對象編程的基礎。
類是對某個對象的定義。它包含有關對象動作方式的信息，包括它的名稱、方法、屬性和事件。實際上它本身並不是對象，因為它不存在於內存中。當引用類的代碼運行時，類的一個新的實例，即對象，就在內存中創建了。雖然只有一個類，但能從這個類在內存中創建多個相同類型的對象。類通過介面與外界發生關係。
可以把類看作「理論上」的對象，也就是說，它為對象提供藍圖，但在內存中並不存在。從這個藍圖可以創建任何數量的對象。從類創建的所有對象都有相同的成員：屬性、方法和事件。但是，每個對象都象一個獨立的實體一樣動作。例如，一個對象的屬性可以設置成與同類型的其他對象不同的值。
希望可以給你在學習Java的路上帶來力所能及的幫助
Java類的定義
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 定義類 如何寫？
類是一種引用數據類型。類為對象的模板，簡單的說就是分類。
類的定義包括「成員變數」的定義和「方法」的定義，其中「成員變數」用於描述一類對象共同的數據結構。在Java語言中，類的成員變數的定義可以使用如下語法：
class 類名 {
成員變數類型變數名稱；
………
}
類是用class關鍵字來定義的一種抽象數據類型，類不但定義了抽象數據類型的組成（成員變數），同時還定義了對該類型可以實施的操作（方法），類名的首字母必須大寫。看如下代碼定義了僱員類:
/** 定義僱員類 */
public class Emp{
String name;
int age;
char gender;
double salary;
}
在如上的實例代碼中，僅僅定義了Emp類型的組成，即成員變數。該類定義了4個成員變數：String類型的name用於存放名字；int類型的age用於存放年齡；char類型的gender用於存放性別；double類型的salary用於存放工資。
原創文章，作者：小藍，如若轉載，請註明出處：https://www.506064.com/zh-tw/n/292059.html
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