Java实例代码.doc

例1.1 / import java.awt.*;import java.applet.Applet;public class SmileFace extends Applet /一个Applet public void paint(Graphics g) g.setColor (Color.yellow); g.fillOval (35, 15, 50, 50); / head g.setColor (Color.black); g.fillOval (50, 30, 5, 5); / left eye g.fillOval (65, 30, 5, 5); / right eye g.drawArc (50, 40, 20, 10, 190, 160); / smile 例2.4（3）public class FunnyNumbers public static void main(String args) double largeNum = (int)Math.exp(4000.0); double posDivZero = 10.0/0; double negDivZero = 10.0 / 0.0; double zeroDivZero = 0.0/0.0; System.out.println(largeNum); System.out.println(posDivZero); System.out.println(negDivZero); System.out.println(zeroDivZero); double x=largeNum+posDivZero; double y=largeNum+negDivZero; double z=largeNum+zeroDivZero; System.out.println(x=+x); System.out.println(y=+y); System.out.println(z=+z); 例2.5public class IncDecTest public static void main(String args) int j, k; System.out.println(第一组:); k = 1; j = k+; System.out.println(j); System.out.println(k); System.out.println(第二组:); k = 1; j = +k; System.out.println(j); System.out.println(k); System.out.println(第三组:); k = 1; System.out.println(k+); System.out.println(+k); System.out.println(k); System.out.println(k); 例2.12if (score = 90) System.out.println(Letter grade: A);else if (score = 80.0) System.out.println(Letter grade: B);else if (score = 70.0) System.out.println(Letter grade: C);else if (score = 60.0) System.out.println(Letter grade D);else System.out.println(Letter grade: F);例2.13switch (grade) case A: case a: System.out.println(90分或更好); break; case B: case b: System.out.println(80到89.99分之间); break; case C: case c: System.out.println(70到79.99分之间); break; case D: case d: case F: case f: System.out.println(少于70分); break; default: System.out.println(无效等级);例2.16public class ArrayParameters public static void changeOrNot(int i, double x) i = -1; x0 = -2.0; double y = x; y1 = -3.0; double z = -4,-4,-4; x = z; public static void main(String args) int k = 1; double A = 1.0, 2.0, 3.0; changeOrNot(k, A); System.out.println(k: + k); System.out.println(A0: + A0); System.out.println(A1: + A1); System.out.println(A2: + A2); 例2.19if (name1.equals(name2) System.out.println(names are the same );else System.out.println(names are different );public class StrangeStrings public static void main(String args) String name1 = 比尔 盖茨;String first = 比尔;String last = 盖茨; String name2 = first + + last; System.out.println(name1); System.out.println(name2); if (name1.equals(name2)/不是if (name1 = name2) System.out.println(names are the same); else System.out.println(names are different); 例2.21import java.io.*;public class Console public static double readDouble() try return Double.valueOf(readString().trim().doubleValue(); catch(NumberFormatException ne) System.err.println(Console.readDouble: Not a double.); System.exit(-1); return 0.0; public static int readInt() try return Integer.valueOf(readString().trim().intValue(); catch(NumberFormatException ne) System.err.println(Console.readInt: Not an integer.); System.exit(-1); return -1; public static String readString() String string = new String(); BufferedReader in=new BufferedReader(new InputStreamReader(System.in); try string = in.readLine(); catch(IOException e) System.out.println(Console.readString: Unknown error.); System.exit(-1); return string; 例3.4class Address / 成员变量 String firstName; String lastName; String email; / 构造方法 Address(String _firstName, String _lastName, String _email) firstName = _firstName; lastName = _lastName; email = _email; / 成员方法 void showAddress() /* 具体实现 */ 例3.5class Parents / 成员变量 String LABELS = father, mother; Address parents = new Address2; / 构造方法 Parents() for (int i = 0; i = 0) & (scale.equals(meter) | (scale.equals(feet) isValid = true; public Length convertToFeet() if (scale.equals(feet) | (!isValid) return this; else return new Length(value * 3.2809, feet); public Length convertToMeter() if (scale.equals(meter) | (!isValid) return this; else return new Length(value / 3.2809, meter); public void showLength() if (isValid) System.out.println(value + + scale); else System.out.println(invalid length); 例3.14public class Length private double value = 0; private String scale = none; private boolean isValid = false; public Length(double _value, String _scale) /* 参考前面例子 */ public Length convertToFeet() /* 参考前面例子 */ public Length convertToMeter() /* 参考前面例子 */ public void showLength() /* 参考前面例子 */ public double getValue() return value; public String getScale() return scale; public boolean isValid() return isValid; public void setValue(double newValue) if (newValue = 0) value = newValue; else isValid = false; public class SafeLengthTest public static void main(String args) Length length = new Length(2, meter); System.out.print(Current: ); length.showLength(); System.out.println(Value: + length.getValue(); System.out.println(Scale: + length.getScale(); System.out.println(Valid: + length.isValid(); System.out.print(To 4 meter: ); length.setValue(4); length.showLength(); 例3.151public class ConcentricCirclesTester2 public static void main(String args)3 ConcentricCircles.x += 100; ConcentricCircles.y += 100;4 ConcentricCircles t1 = new ConcentricCircles();5 ConcentricCircles t2 = new ConcentricCircles(); 6 t1.x += 100;7 t1.r = 50;8 t2.y += 100;9 t2.r += 150;10 System.out.println(T1: x = + t1.x + , y = + t1.y + , r = + t1.r);11 System.out.println(T2: x = + t2.x + , y = + t2.y + , r = + t2.r);12 13例3.17public class CountingObject public static int counter = 0; public CountingObject() counter+; System.out.println(= 创建第 + counter +个对象); public void finalize() System.out.println(= 清除第 + counter+个对象); counter-; public class ObjectCounter public static String showMenu() System.out.println(reate object); System.out.println(un garbage collector); System.out.println(Exit the program); System.out.print(Enter choice: ); return Console.readString(); public static void main(String args) CountingObject obj = null; String choice = showMenu(); while (!choice.equalsIgnoreCase(x) if (choice.equalsIgnoreCase(c) obj = new CountingObject(); else if (choice.equalsIgnoreCase(r) System.gc(); choice = showMenu(); 例3.19public class Student private String name; private double GPA; public Student() this(无名氏, -1.0); /一个不知姓名和GPA的学生对象 public Student(String _name) this(_name, -1.0); /知道姓名不知GPA的学生对象 public Student(double _GPA) this(无名氏, _GPA); /知道GPA但不知姓名的学生对象 public Student(String _name, double _GPA) name = _name; GPA = _GPA; /知道姓名和GPA的学生对象 public void showStudent() System.out.print(Student: + name); if (GPA = 0.0) System.out.println( (GPA: + GPA + ); else System.out.println(); 例3.21public class Shape protected String name; protected double area, perimeter; public Shape() name = undetermined; area = perimeter = 0; public void display() System.out.println(Name: + name); System.out.println(Area: + area); System.out.println(Perimeter: + perimeter); public class Rectangle extends Shape protected double length, width; public Rectangle(double _length, double _width) name = Rectangle; length = _length; width = _width; public void computeArea() area = length * width; public void computePerimeter() perimeter = 2*(length + width); public class Circle extends Shape protected double radius; public Circle(double _radius) name = Circle; radius = _radius; public void computeArea() area = Math.PI * radius * radius; public void computePerimeter() perimeter = 2 *Math.PI * radius; public class ShapeTester public static void main(String args) Shape s = new Shape(); Rectangle r = new Rectangle(2.0, 3.); Circle c = new Circle(4.0); puteArea(); putePerimeter(); puteArea(); putePerimeter(); r.display();c.display(); s.display(); 例3.25ublic class Shape protected String name; protected double area, perimeter; public Shape() name = undetermined; area = perimeter = 0; public void display() System.out.println(* GEOMETRIC SHAPE *); System.out.println(name+, area +area+, perimeter +perimeter); 例3.27public class Rectangle extends Shape protected double length, width; public Rectangle(double _length, double _width) name = Rectangle; length = _length; width = _width; final public void computeArea() area = length * width; public void computePerimeter() perimeter = 2*(length + width); public final class Circle extends Shape protected double radius; public Circle(double _radius) name = Circle; radius = _radius; final public void computeArea() area = Math.PI * radius * radius; final public void computePerimeter() perimeter = 2 *Math.PI * radius; public final class Square extends Rectangle public Square(double _side) super(_side, _side); name = Square; 例328public class ShapeTester / main 方法 public static void main(String args) Rectangle r = new Rectangle(2.0, 3.); Circle c = new Circle(4.0); puteArea(); putePerimeter(); puteArea(); putePerimeter(); System.out.println(r); System.out.println(c); 例3.29public class ObjectArray public static void display(Object obj) if (obj instanceof Rectangle) System.out.println( (Rectangle)obj).toString(); else if (obj instanceof Circle) System.out.println( (Circle)obj).toString(); else if (obj instanceof Double) System.out.println( (Double)obj).toString(); else if (obj instanceof Integer) System.out.println( (Integer)obj).toString(); public static void main(String args) Object objects = new Object4; objects0 = new Rectangle(); objects1 = new Circle(); objects2 = new Double(1.0); objects3 = new Integer(2); for (int i = 0; i objects.length; i+) display(objectsi); 例3.30public class SuperSuper public SuperSuper() System.out.println(SuperSuper Class); public class Super extends SuperSuper public Super() System.out.println(Super Class); public class Sub extends Super public Sub() System.out.println(SubClass); public class Test public static void main(String args) Sub c = new Sub(); 例3.32public abstract class Shape protected String type; protected double area, perim; public abstract void computeArea(); public abstract void computePerimeter(); public String toString() return type + :ntArea = + area + ntPerimeter = + perim; public class Rectangle extends Shapepublic class Circle extends Shape protected double width, height; protected double radius; public Rectangle(double _width, public Circle(double _radius) double _height) type = Circle; type = Rectangle; radius = _radius; width = _width; height = _height; public void computeArea() area = Math.PI * radius * radius; public void computePerimeter() public void computeArea() perim = 2.0 * Math.PI * radius; area = width * height; public String toString() public void computePerimeter() return super.toString() + perim = 2*width + 2*height; ntRadius = + radius; public String toString() return super.toString() + ntWidth = + width + ntHeight = + height; public class Square extends Rectangle public Square(double _side) super(_side, _side); type = Square; 例3.33package graphicPackage;/在Graphic.java中的文件的第一行public abstract class Graphic public class Circle extends Graphic implements Draggable public class Rectangle extends Graphic implements Draggable public interface Draggable /* File: ErsBox.java * Describe: 俄罗斯方块的 Java 实现 */import java.awt.*;class ErsBox implements Cloneable private boolean isColor;private Dimension size = new Dimension();/* 方格类的构造方法 * param isColor 是不是用前景色来为此方格着色 * true前景色，false用背景色 */public ErsBox(boolean isColor) this.isColor = isColor;/* 此方格是不是用前景色显示 * return boolean, true用前景色显示，false用背景色显示 */public boolean isColorBox() return isColor;/* 设置方格的颜色， * param isColor boolean, true用前景色显示，false用背景色显示 */public void setColor(boolean isColor) this.isColor = isColor;/* 获得此方格的尺寸 * return Dimension,方格的尺寸 */public Dimension getSize() return size;/* 设置方格的大小 * param size Dimension,方格的大小 */public void setSize(Dimension size) this.size = size;/* 覆盖Object的Object clone()方法，实现克隆 * return Object,克隆的结果 */public Object clone() /如前所示例4.1import java.io.File;public class FileMethodDemostatic void print(String s) System.out.print(s);public static void main(String args)File f = new File(C:/jdk/bin/java.exe);/建立文件类print(文件名称: + f.getName() + n);/取得文件名称print(文件路径: + f.getPath() + n);/取得文件路径print(绝对路径: + f.getAbsolutePath() + n);/取得绝对路径print(上级目标: + f.getParent() + n);/取得上级目录名称print(文件大小: + f.length() + bytesn);/取得文件大小print(最后修改时间: + f.lastModified() + n);/取得最后修改时间print(是否存在:);print(f.exists() ? 存在n : 不存在n);/检查是否存在print(是否可读取:);print(f.canRead() ? 可读取n : 不可读取n);/检查是否可读取print(是否可写入:);print(f.canWrite() ? 可写入n : 不可写n);/检查是否可写入 例4.2import java.io.File;public class DirectoryDemostatic v