吃不饱的刘某人

吃不饱的刘某人

• • Who say what
  • 算术运算符的使用
  • 位运算符的使用
  • 关系运算符的使用
  • 逻辑运算符的使用
  • 数据类型转换
  • 全局变量和局部变量
  • 比较两个数的大小
  • 给成绩评定等级
  • 计算数学分段函数
  • 使用switch给成绩评定等级
  • 10的阶乘
  • 求和1+1/2-1/3+......+1/100
  • 求和1！+2！+3！+4！+5！
  • 用do-while计算10！
  • 求50~100之间所有素数的程序，目的是演示一下break语句的使用
  • 使用continue语句，计算10以内的奇数的和
  • 计算四位数，前两位一样，后两位一样
  • 判断一个正整数是否是素数，若是计算其阶乘
  • 创建对象与field的访问
  • 简单数据类型作参数,计算立方体体积
  • 圆形类CCircle，计算圆的面积
  • 对象类型作参数
  • 参数的单向值传递
  • 共有成员(method)的建立
  • 私有成员无法从类外部来访问的范例
  • 构造方法的定义与使用
  • static定义静态变量
  • 通过类名访问类方法
  • 建立获取对象名字的成员方法getName和获取对象性别的成员方法getSex，以及输出对象的全部成员方法studPrint
  • 从一组号码1，2，3……high中，抽出一组幸运号码，将幸运号码作为方法的返回值返回
  • 求一维数组的最大值和最小值
  • 二维数组的赋值与输出
  • 求二维数组的最大值
  • 三维数组
  • 子类可以继承父类的所有非私有数据成员
  • 子类中的同名属性对父类同名属性的隐藏
  • 子类同名方法对父类同名方法的覆盖
  • 子类对父类方法的继承
  • super的使用
  • 方法的重载
  • 构造方法的继承
  • 构造方法的重载
  • 抽象类的实例
  • 用抽象类类型的变量来建立对象
  • 利用父类的变量数组来访问子类里的内容
  • 接口的实现范例
  • 实现两个以上的接口
  • 接口的扩展
  • 在构造函数里建立内部类的对象
  • final修饰数据成员
  • final修饰的最终方法
  • System的范例：请输入一个字符
  • object类的范例
  • 数学类
  • 字符串类
  • 判断大小写
  • Calendar类的应用范例
  • Random类的范例。随机产生1~6之间的随机整数，统计各数出现的概率
  • 一个简单的框架窗口
  • 通过继承JFrame类实现的窗口（疑惑？）
  • 向框架窗口中添加按钮组件
  • BorderLayout的布局的应用
  • GridLayout布局的应用
  • 向FlowLayout布局的容器中添加多个大小不同的组件
  • 通过容器的嵌套实现较复杂的布局
  • text（you click the button ok）

Who say what

//WhoSayWhat.java
class WhoSayWhat {public static void main(String args[ ]) { if(args.length < 2) {System.out.println("请向应用程序传递两个参数");System.exit(0);}String s1 = args[0];String s2 = args[1];System.out.println(s1 + " Say：" + s2);}
}

算术运算符的使用

public class ArithOp {public static void main(String[ ] args)  {int a = 7 + 2;     int b = a*2;	       int c = b / 9;          int d = - a;           int e = d % 2;        double f = 17.5 / 4;    int i = 2;int j = i ++;         int k = ++ i;        System.out.println("a=" + a);System.out.println("b=" + b);System.out.println("c=" + c);System.out.println("d=" + d);System.out.println("e=" + e);System.out.println("f=" + f);System.out.println("i=" + i);System.out.println("j=" + j);System.out.println("k=" + k);}
}

位运算符的使用

public class BitOp {public static void main(String[ ] args) {int a = 9;         //二进制数1001int b = 15;        //二进制数1111	int c = 8;         //二进制数1000  int d,e,f,g,h;d = a & b;      //二进制数1001,也就是十进制数9e = a | b;       //二进制数1111,也就是十进制数15f = a ^ b;       //二进制数0110,也就是十进制数6g = a << 2;     //  9*4=36  h = c >> 1;     //  8/2=4;System.out.println("d=" + d);System.out.println("e=" + e);System.out.println("f=" + f);System.out.println("g=" + g);System.out.println("h=" + h);}
}

关系运算符的使用

public class RelationOp {public static void main(String[ ] args) {
int a = 9;  int b = 6;		int c = 6;      boolean d = a > b;      //trueboolean e = a < b;      //falseboolean f = b == c;     //trueboolean g = b != c;     //falseboolean h = b >= c;     //trueboolean i = b <= c;     //true boolean j = a == b;     //falseSystem.out.println("d=" + d);System.out.println("e=" + e);System.out.println("f=" + f);System.out.println("g=" + g);System.out.println("h=" + h);System.out.println("i=" + i);System.out.println("j=" + j);}
}

逻辑运算符的使用

public class LogicOp {public static void main(String[ ] args) {int a = 9;  int b = 6;		int c = 6;      boolean d,e,f,g;d = ! (a > b);            //falsee = (a > b) && (a > c);     //truef = (b == c) || (a < b);      //trueg = (b == c) && (a < b);   //falseSystem.out.println("d=" + d);System.out.println("e=" + e);System.out.println("f=" + f);System.out.println("g=" + g);}
}

数据类型转换

public class TypeConversion {public static void main(String[ ] args) {char a = 1;byte b = 2;short c = 3; int d = 4;byte e;e = (byte)(a + b + c + d);  //将"a+b+c+d"的值强制转化为byte型//如果写成“e = a + b + c + d;”，将出错short f;f = (short)(a + b + c + d);  //将"a+b+c+d"的值强制转化为byte型//如果写成“f = a + b + c + d;”，将出错int g;g = a + b + c + d;          //a,b,c,d自动转换为int型再计算float h;　　　　h = a + b + c + d;          //a,b,c,d自动转换为float型再计算double i;i = a + b + c + d;          //a,b,c,d自动转换为double型再计算System.out.println("e = " + e);System.out.println("f = " + f);System.out.println("g = " + g); System.out.println("h = " + h);System.out.println("i = " + i);}
}

全局变量和局部变量

public class SetVariable
{	//全局变量
static double pi = 3.141592654；//数学常量
static short s1;static int i1;static long l1;static char ch1;static float f1;static double d1;static boolean b1;public static void main(String args[]){//局部变量short s2 = 35;int i2 = -32;long l2 = 34555L;char ch2 = 'A';float f2 = 897.89F;double d2 = 34.345;boolean b2 = false;//输出常量System.out.println("数学常量pi = " + pi);//输出局部变量System.out.println("******局部变量******");System.out.println("短整型变量s2 = " + s2);System.out.println("整型变量i2 = " + i2);System.out.println("长整型变量l2 = " + l2);System.out.println("字符变量ch2 = " + ch2);System.out.println("浮点数类型f2 = " + f2);System.out.println("双精度型变量d2 = " + d2);System.out.println("布尔型变量b2 = " + b2);         //调用方法修改全局变量的值change();//输出全局变量的值System.out.println("******全局变量******");System.out.println("短整型变量s1 = " + s1);System.out.println("整型变量i1 = " + i1);System.out.println("长整型变量l1 = " + l1);System.out.println("字符变量ch1 = " + ch1);System.out.println("浮点数类型f1 = " + f1);System.out.println("双精度型变量d1 = " + d1);System.out.println("布尔型变量b1 = " + b1);}//方法：修改全局变量的值public static void change(){s1 = 125;i1 = 88;l1 = 987654321L;ch1 = 'B';f1 = 3.2590F;d1 = -1.04E-5;b1 = true;}
}

比较两个数的大小

public class  Ifdemo1 {public static void main(String[ ] args) {int i1 = 8, i2 = 5;if(i1 >= i2)System.out.println(i1 + ">=" + i2);elseSystem.out.println(i1 + "<" + i2);      }
}

给成绩评定等级

public class IfDemo2 {
public static void main(String[ ] args) {int testscore = 78; char grade;if (testscore >= 90) grade = 'A';else if (testscore >= 80)grade = 'B';else if (testscore >= 70) grade = 'C';else if (testscore >= 60) grade = 'D';else grade = 'E';System.out.println("Grade = " + grade);  }
}

计算数学分段函数

public class  Ifdemo3 {public static void main(String[ ] args) {int  x = 4;float y;if(x <= 0)y = x + 8;else if(x <= 6)y = 3 * x-21;elsey = 8 * x * x - 9;System.out. println("y = " + y);}
}

使用switch给成绩评定等级

public  class  SwitchDemo {public static void main(String[ ] args) {int testscore = 78;char grade;switch(testscore / 10) {case 10:case 9: grade = ' A'; break;case 7: grade = 'C'; break;case 6: grade = 'D'; break;default: grade = 'E';}System.out.println("Grade = " + grade);}
}

10的阶乘

public class ForOp1 {public static void main(String[ ] args)	{long result = 1;for(int i = 10; i > 0; i--)result *= i ;System.out.println("10!=" + result);}
}

求和1+1/2-1/3+…+1/100

public class ch2 {
public static void main(String[ ] args) {
int m = 1;double s = 0;for(int i = 1;i <= 100;i ++) {s = s + m * 1.0 / i;m = - m;}System.out.println("s =" + s);}
}

求和1！+2！+3！+4！+5！

public  class  ch3n {public static void main(String[ ]  args) {int i,t,s=0;for(i = 1,t = 1;i <= 5;i ++) {t = t *i;s + = t;}System.out.println(" s =  " + s);}
}

用do-while计算10！

//用do - while语句计算10的阶乘。
public class DoWhileDemo {public static void main(String[ ] args)	{int n = 10;long result = 1;doresult * = n--;while(n >= 1);System.out.println("10!=" + result);}
}

//用while语句计算10的阶乘。
public class WhileDemo {public static void main(String[ ] args)	{int n = 10;long result = 1;while(n >= 1)result * = n--;System.out.println("10! = " + result);}
}

求50~100之间所有素数的程序，目的是演示一下break语句的使用

public class Prime50_100Exam{public static void main(String[] args) {int n,m,i;for( n=50; n<100; n++){for( i=2; i<=n/2; i++){if(n%i==0)  break;  //被i除尽，不是素数，跳出本循环}if(i>n/2)   //若i>n/2,说明在上边的循环中没有遇到被除尽的数{System.out.print(n+"  ");  //输出素数}}}
}

使用continue语句，计算10以内的奇数的和

public class ContinueOp{public static void main(String[ ] args){int  s = 0;for(int i = 1;i <=10;i ++) {if (i % 2 == 0)  continue;s += i ;}System.out.println("s = " + s);}
} 

计算四位数，前两位一样，后两位一样

public class first {public static void main(String[] args) {int a,i,x,y,z,t;for( i=32; i<100; i++){   a=i*i;x=a/1000;    //千位y=a/100%10;  //百位z=a/10%10;   //十位t=a%10;      //个位if(x==y&&z==t){ System.out.print(i+"的平方是"+a);}}}
}

判断一个正整数是否是素数，若是计算其阶乘

/**该程序包含以下两个方法，prime() 方法判断一个整数是否为素数，factorial()方法用于求一个整数的阶乘，目的是演示return语句的应用*/
public class Math_mothodExam{public static boolean prime(int n){  //判断n是否素数方法for(int i=2; i<n/2; i++){if(n%i==0)  return false; //n不是素数}return true; //n是素数}  //prime()方法结束public static int factorial(int n){ //求阶乘方法if(n<=1) return 1;int m=1;for(int i=1; i<=n; i++) m*=i;return m;} //factorial()方法结束public static void main(String args[]){ //主方法int n=13;System.out.println(n+"是素数吗？"+prime(n));if(prime(n)) System.out.println(n+"!="+factorial(n));} 
}

创建对象与field的访问

class CRectangle{    // 定义CRectangle类int width;         // 声明数据成员width int height;        // 声明数据成员height
}
public class app7_1{public static void main(String args[]){CRectangle rect1;rect1=new CRectangle();    // 创建新的对象rect1.width=10;    // 赋值长方形rect1的宽rect1.height=5;    // 赋值长方形rect1的高System.out.println("width="+rect1.width); //   输出rect1.widthSystem.out.println("height="+rect1.height); //   输出rect1.height}
}

简单数据类型作参数,计算立方体体积

class cube{double width;double height;double depth;double volume() {                       //定义计算立方体体积的方法return width * height * depth;}void setParam(double  x,double  y,double  z) {width = x;                      //定义设置立方体三维数值的方法    height = y;depth = z;}}        
public class Usecube {public static void main(String args[ ]) {double v;cube  mycube = new cube();mycube.setParam(4,6,8);v = mycube.volume();System.out.println("mycube.volume = " + v);}} 

圆形类CCircle，计算圆的面积

class CCircle   // 定义类CCircle
{double pi;    // 将数据成员赋值初值 double radius;double getRadius(){return radius;}void setCircle(double r, double p){     pi=p;radius=r;   }
}public class Ccircle_main
{public static void main(String args[]){CCircle cir1=new CCircle();   //  声明并建立新的对象cir1.setCircle(2.0,3.1416);System.out.println("radius="+cir1.getRadius()); }
}  

对象类型作参数

class Point {int x,y;
}
class Carry{void fun(Point p) {p.x += p.y;p.y *= 5;}	
}
public class UsePoint {public static void main(String args[ ]){carry s = new carry();point p = new Point();p.x = 3;p.y = 5;s.fun(p);System.out.println("p.x = " + p.x + ", p.y = " + p.y);}
}

参数的单向值传递

public class  Carry {static void fun(int x,int y) {x = x + y;y = 5 * y;System.out.println("x = " + x + ", y = " + y); }public static void main(String args[ ]) {int  a = 3;int  b = 5;fun(a,b);System.out.println("a = "+a+", b = " + b);}
}

共有成员(method)的建立

class CCircle   // 定义类CCircle
{private double pi=3.14;    // 将数据成员设置为privateprivate double radius;public void show_area(){   // 将method设置为publicSystem.out.println("area="+pi*radius*radius);}public void setRadius(double r){  if(r>0){radius=r;      // 将私有成员radius设为rSystem.out.println("radius="+radius);}elseSystem.out.println("input error");}  
}public class Gongyou
{public static void main(String args[]){CCircle cir1=new CCircle();  cir1.setRadius(-2.0);cir1.show_area();}
}

私有成员无法从类外部来访问的范例

class CCircle   // 设置field为私有成员
{private double pi=3.14;    // 为数据成员设置初值 private double radius;void show_area(){  System.out.println("area="+pi*radius*radius);  //在CCircle类内部，故可访问私有成员}
}
public class Siyou
{public static void main(String args[]){CCircle cir1=new CCircle();cir1.radius=-2.0; //错误：在CCircle类外部，无法直接更改私有成员。更改radius定义中的private即可，改为publiccir1.show_area();}
} 

构造方法的定义与使用

class Dog {private int weight;public Dog() {     //构造方法weight = 42; }public int getWeight() {return weight;}}
public  class UseDog {public static void main(String args[ ]) {Dog d = new Dog();System.out.println("The dog’s weight is " + d.getWeight());}}

static定义静态变量

class SDemo {int x;static int y;
}
public class StaticDemo {public static void main(String arg[ ]) {SDemo  ob1 = new SDemo();SDemo  ob2 = new SDemo();ob1.x = 10;ob2.x = 20;System.out.println("Of course ,ob1.x and ob2.x "+ob1.x+ob2.x);System.out.println("The static var is shared");ob1.y = 19;System.out.println("ob1.y=" + ob1.y);System.out.println("ob2.y=" + ob2.y);//类的static成员是公用的SDemo.y = 11;  //通过类名引用static成员System.out.println("SDemo.y = " + SDemo.y);System.out.println("ob1.y = " + ob1.y);System.out.println("ob2.y = " + ob2.y);}
}	

通过类名访问类方法

class SMeth{static int val=1024;static int valDiv2(){return val / 2;}}		
public class Staicmeth {public static void main(String args[ ]) {System.out.println("Val is" + SMeth.val);System.out.println("StaticMeth.valDiv2():" + SMeth.valDiv2());}
}

建立获取对象名字的成员方法getName和获取对象性别的成员方法getSex，以及输出对象的全部成员方法studPrint

/*设有若干个学生，每个学生有姓名、性别和成绩三个属性， 要求将每个学生作为一个对象，建立获取对象名字的成员方法getName和获取对象性别的成员方法getSex，以及输出对象的全部成员方法studPrint。
*/
class Student {private String name;private char sex;private double score;Student (String cname,char csex,double cscore) {name = cname;sex = csex;score = cscore;}String getName() {return name;}char getSex() { return sex; }void studPrint() {System.out.println("Name:" + name +  "\tSex:" + sex + "\tScore:" + score); }
}
public class rrOb {public static void main(String args[ ]) {String mname;char msex;int len;Student[ ] st1 = new Student[3];st1[0] = new Student("Li", 'F',89);st1[1] = new Student("Zhang", 'M',90);st1[2] = new Student("Zhou", 'F',98);for(int i = 0; i < st1.length; i ++)st1[i].studPrint();mname = st1[1].getName();msex = st1[1].getSex();System.out.println("Name 1:" + mname + "\t" + msex);}
}

从一组号码1，2，3……high中，抽出一组幸运号码，将幸运号码作为方法的返回值返回

/*RandomA.java   从一组号码1，2，3……high中，抽出一组幸运号码，将幸运号码作为方法的返回值返回。drawing方法//的返回值为一个数组。*/
import java.util.Arrays;
public  class RandomA {public static int [ ] drawing(int high,int number) {int I;int numbers[ ] = new int [high];int result[ ] = new int [number];for(i = 0;i < high;i ++)numbers[I] = i +1; for(i = 0;i < number;i ++) {int j = (int)(Math.random()*(high-i));result[i] = numbers[j];numbers[j] = numbers[high-1-i];}return result;}public static  void main(String args[ ]) {int numbers = 7;int topNumber = 36;int a[ ] = drawing(topNumber,numbers);Arrays.sort(a);  //java.lang.Arrays中提供的数组排序方法System.out.print("Lucky numbers are: ");for(int i = 0;i < a.length; i ++)System.out.print(" " + a[i]);System.out.println();}
}

求一维数组的最大值和最小值

public class Arraymax {public static void main(String args[ ]) {int table[ ] = {21,34,65,38,24,46,29,64,75,92};int i,max,min;System.out.print("Table:  ");for(i = 0;i < table.length;i ++)System.out.print("  " + table[i]);System.out.println();max =min = table[0];for(i = 1; i < table.length; i ++){if(table[i] > max)max = table[i];else if(table[i] < min)min = table[i]; }System.out.println("Max=" + max);System.out.println("Min=" + min);}
}

二维数组的赋值与输出

public class ArrIO {public static void main(String args[ ]) {int a[ ][ ] = new int[4][ ];for(int I = 0;I < a.length;I ++) {a[I] = new int[5];for(int j = 0;j < a[I].length;j ++)a[I][j] = I+j;}for(int k = 0;k < a.length;k ++) {for(int n = 0;n< a[k].length;n ++)System.out.print("a["+k+"]["+n+"]=" + a[k][n] + "  ");            System.out.println();}} 
}

求二维数组的最大值

class Maxvalue {int maxv(int arr1[ ][ ]) {int i,j,max;max = arr1[0][0];for(i = 0; i < arr1.length; i ++)for( j = 0;j < arr1[i].length; j ++)if(arr1[i][j] > max)max = arr1[i][j];return max;}
}
public class ArrMax {public static void main(String args[ ]) {int a[ ][ ] ={{1,3,5},{2,5,7,8},{8,3,4,6,9}};int max;Maxvalue p = new Maxvalue();max = p.maxv(a);System.out.println("max=" + max);}
}

三维数组

public class Sanwei{public static void main(String args[]){                int i,j,k,sum=0;int A[][][]={{{5,1},{6,7}},{{9,4},{8,3}}}; // 声明数组并设置初值for(i=0;i<A.length;i++)	// 输出数组内容并计算总和for(j=0;j<A[i].length;j++)for(k=0;k<A[j].length;k++){System.out.print("A["+i+"]["+j+"]["+k+"]=");System.out.println(A[i][j][k]);sum+=A[i][j][k];}System.out.println("sum="+sum);}
}

子类可以继承父类的所有非私有数据成员

class A1{int x = 25;private int z;  //不能被子类继承的私有数据成员
}
public  class SubDemo1 extends A1{public static void main(String args[ ]) {subDemo1 p = new subDemo1();System.out.println("p.x = " + p.x);  //子类继承了父类的成员System.out.println(“p.z = ” + p.z);  //编译错，不能继承父类的私有成员}
}

子类中的同名属性对父类同名属性的隐藏

class  A {int x1 = 10;float x2 = 2.0f;
}
class B extends A {int x1 = 15;int x2 = 25;String x3 = "hello";
}
public class C {public static void main(String args[ ]) {A  p1 = new A();B  p2 = new B();System.out.println("A:" + p1.x1 + p1.x2);System.out.println("B:" + p2.x1 + p2.x2 + p2.x3);}
}

子类同名方法对父类同名方法的覆盖

class  A  {int fun(int  a,int  b) {return  a * b;}
}
class B extends  A {int fun(int c,int d) {return c + d;}
}
public class C2 {public static void main(String args[ ]) {B s = new B();System.out.println("s = " + s.fun(10,20));}
}

子类对父类方法的继承

class A2 {int x = 0,y = 1;void print1() {System.out.println("x = " + x + "y = " + y);}private void print2() {System.out.println("x = " + x + "y = " + y);}}
public class SubDemo2 extends A2 {public static void main(String args[ ]) {int z = 3;SubDemo2 p = new SubDemo2();p.print1();  //子类继承父类的方法p.print2();  //错，子类不能继承父类的私有方法}}

super的使用

//SuperDemo.java  
class A {int x1 = 10;float x2 = 2.0f;void show(){System.out.println("1 A:" + "x1  =  " + x1 + "x2  =  " + x2);
}}
class B extends  A {int x1 = 15;int x2 = 25;void show() {System.out.println("2 A:" + "x1 = " + super.x1 + "x2 = " + super.x2);//调用父类成员变量super.show(); //调用父类的成员方法System.out.println("3 B:" + "x1 = "+ x1 + "x2 = " + x2);
}}
public class SuperDemo {public static void main(String args[ ]) {A  p = new A();B  q = new B();p.show();q.show();}
}

方法的重载

class A {int add(int a,int b) {return a + b;}double add(double a,double  b) {return a + b;}double add(double a,double b,double  c) {return a + b + c;}
}
public class OverloadDemo {public static void main(String args[ ]) {A p = new A();System.out.println("Sum is " + p.add(3.8,5.3));System.out.println("Sum is " + p.add(3,5));System.out.println("Sum is " + p.add(3.8,5.3,7.2));}
}

构造方法的继承

class AddClass {public int x = 0,y = 0,z = 0;AddClass (int x) { //父类可重载的构造方法1this.x = x;} AddClass (int x,int y){ // 父类可重载的构造方法2this.x = x;this.y = y;}AddClass (int x,int y,int z){// 父类可重载的构造方法3this.x = x;this.y = y;this.z = z;}public int add() {return x + y + z;}
}
public class Subconstruct  extends AddClass {int a = 0,b = 0,c = 0;Subconstruct(int x) { super(x);  //调用父类的构造方法1a = x + 7;}Subconstruct(int x,int y) {super(x,y);  //调用父类的构造方法2a = x + 5;b = y + 5;}Subconstruct(int x,int y,int z) { //调用父类的构造方法3super(x,y,z);a = x + 4;b = y +4;c = z + 4;}public int add() {System.out.println("super: x + y + z = " + super.add());return a + b + c;}public static void main(String args[ ]) {Subconstruct p1 = new Subconstruct (2,3,5);Subconstruct p2 = new Subconstruct (10,20);Subconstruct p3 = new Subconstruct (1);System.out.println("a + b + c = " + p1.add());System.out.println("a + b= " + p2.add());System.out.println("a = " + p3.add());}
}

构造方法的重载

// ConstructOver.java
class AddClass {public int x = 0,y = 0,z = 0;AddClass (int x) {  //构造方法1this.x = x;  //this.x为本类的成员属性}AddClass (int x,int y) {  //构造方法2this(x);  //调用本类的构造方法1this.y = y;}AddClass (int x,int y,int z){ //构造方法3this(x,y);this.z = z;}public int add() {return  x+y+z;}
}
public class ConstructOver {public static void main(String args[ ]) {AddClass p1 = new AddClass (2,3,5);AddClass p2 = new AddClass (10,20);AddClass p3 = new AddClass (1);System.out.println(" x + y + z = " + p1.add());System.out.println(" x + y = " + p2.add());System.out.println(" x = " + p3.add());}
}

抽象类的实例

abstract class CShape    //定义抽象类CShape    
{protected String color;public void setColor(String str){color=str;}abstract void show();   // 只声明show()，但没有定义处理方法
}class CRectangle extends CShape    // 定义子类CRectangle
{int width,height;public CRectangle(int w,int h){width=w;height=h;}public void show(){   // 明确定义继承自抽象类的Show() methodSystem.out.print("color="+color+",  ");System.out.println("area="+width*height);      }
}class CCircle extends CShape   // 定义子类CCircle
{double radius;public CCircle(double r){radius=r;}public void show(){     // 明确定义继承自抽象类的Show() methodSystem.out.print("color="+color+",  ");System.out.println("area="+3.14*radius*radius);      }
}public class app1{public static void main(String args[]){CRectangle rect=new CRectangle(5,10);  rect.setColor("Yellow");  // 调用父类里的setColor() methodrect.show();   // 调用CRectangle类里的show() methodCCircle cir=new CCircle(2.0);  cir.setColor("Green");    // 调用父类里的setColor() method cir.show();     // 调用CCircl类里的show() method }
}

用抽象类类型的变量来建立对象

public class app2{public static void main(String args[]){CShape shape1=new CRectangle(5,10); shape1.setColor("Yellow");shape1.show();CShape shape2=new CCircle(2.0); shape2.setColor("Green"); shape2.show(); }
}

利用父类的变量数组来访问子类里的内容

public class app3
{public static void main(String args[]){CShape shape[];   // 声明CShape类型的数组变量shape=new CShape[2];  // 产生两个CShape抽象类类型的变量shape[0]=new CRectangle(5,10); shape[0].setColor("Yellow");shape[0].show();shape[1]=new CCircle(2.0); shape[1].setColor("Green"); shape[1].show(); }
}

接口的实现范例

interface iShape2D{   //定义接口 final double pi=3.14;abstract void area();
}class CRectangle implements iShape2D{    // 实现CRectangle类int width,height;public CRectangle(int w,int h){width=w;height=h;}public void area(){   // 定义area()的处理方式System.out.println("area="+width*height);      }
}class CCircle implements iShape2D{  // 实现CCircle类double radius;public CCircle(double r){radius=r;}public void area(){    // 定义area()的处理方式System.out.println("area="+pi*radius*radius);      }
}public class app4{public static void main(String args[]){CRectangle rect=new CRectangle(5,10);  rect.area();   //调用CRectangle类里的area() methodCCircle cir=new CCircle(2.0);  cir.area();     // 调用CCircl类里的area() method }
}

实现两个以上的接口

interface iShape2D   // 定义iShape2D接口
{final double pi=3.14;abstract void area();
}interface iColor   // 定义iColor接口
{abstract void setColor(String str);
}class CCircle implements iShape2D,iColor  // 实现iShape2D与iColor接口
{double radius;String color;public CCircle(double r){radius=r;}public void setColor(String str){  // 定义iColor接口里的setColor()color=str;System.out.println("color="+color); }public void area(){     // 定义iShape2D接口里的area() methodSystem.out.println("area="+pi*radius*radius);      }
}public class app5
{public static void main(String args[]){CCircle cir;cir=new CCircle(2.0); cir.setColor("Blue");  // 调用CCircl类里的setColor() methodcir.area();     // 调用CCircl类里的show() method }
}

接口的扩展

interface iShape  // 定义iShape接口
{final double pi=3.14;   abstract void setColor(String str);
}interface iShape2D extends iShape   // 定义iShape2D接口, 继承自iShape
{abstract void area();
}class CCircle implements iShape2D  // 实现iShape2D接口
{double radius;String color;public CCircle(double r){radius=r;}public void setColor(String str){ // 定义iShape接口的setColor() methodcolor=str;System.out.println("color="+color); }public void area(){     // 定义iShape2D接口的area() methodSystem.out.println("area="+pi*radius*radius);      }
}public class app6
{public static void main(String args[]){CCircle cir;cir=new CCircle(2.0); cir.setColor("Blue"); cir.area();     // 调用CCircl类里的show() method }
}

在构造函数里建立内部类的对象

public class inner{public inner(){Caaa aa= new Caaa();aa.set_num(5);}public static void main(String args[]){  inner obj=new inner(); // 调用构造函数inner()建立外部类的对象}class Caaa{int num;void set_num(int n){num=n;System.out.println("num= "+ num); }}   
}

final修饰数据成员

class  ca {static int n = 20;final int nn;         //声明nn，但没有赋初值final int k = 40;  //声明k，赋初值40ca() {nn = + + n;}
}
public  class finalDemo1 {public static void main(String args[ ]) {ca  m1 = new ca();ca  m2 = new ca();m1.nn = 90;  //错误的语句，不能在此给最终数据成员赋值System.out.println("m2.nn = " + m2.nn);System.out.println("m2.k = " + m2.k);System.out.println("m1.nn = " + m1.nn);System.out.println("m1.k = " + m1.k);}
}

final修饰的最终方法

class  a1 {final int add(int x,int y) {return x + y;}int mul (int a,int b) {int z = 0;  z = add(1,7) + a * b;  return z;}
}
public class finalDemo2 extends a1 {int  add(int x,int y) {  //此方法非法，企图覆盖父类的的final方法return x + y + 2;} public static void  main(String args[ ]) {int a = 2,b = 3,z1,z2;finalDemo2 p1 = new finalDemo2();z1 = p1.add(a,b);//子类可以引用父类的final方法z2 = p1.mul(a,b);  System.out.println("z1 = " + z1);System.out.println("z2 = " + z2);}
}

System的范例：请输入一个字符

// SystemD.java
public class SystemD {public static void main(String args[ ]) throws Exception {char c;System.out.println("请输入一个字符:");c = (char)System.in.read();System.out.println("你输入字符:" + c);}
}

object类的范例

public class ObjectD {public static void main(String[ ] args) {Integer a = new Integer(1);Integer b = new Integer(1);System.out.println(a.equals(b));System.out.println("The Object’s class is: " + a.getClass());} 
}

数学类

class MathD {public static void main(String args[ ]) {System.out.println("Math.E=" + Math.E);System.out.println("Math.PI=" + Math.PI);System.out.println("sin(pi/2) =" + Math.sin(Math.PI/2));System.out.println("ceil(E)=" + Math.ceil(Math.E));   //返回不小于参数的最小整数System.out.println("rint(PI)=" + Math.rint(Math.PI));   //返回最接近参数的整数System.out.println("round(PI)=" + Math.round(Math.PI));  //返回最接近参数的long型int I = (int)(Math.random()*10) + 1;System.out.println("i =" + i );System.out.println("exp(1)=" + Math.exp(1));System.out.println("lnE=" + Math.log(Math.E));System.out.println("sqrt(" + 25 + ")=" + Math.sqrt(25));System.out.println("power(" + 2 + "," + 8 + ")=" + Math.pow(2,8));// 返回a的b次方System.out.println("abs(-8.2)=" + Math.abs(-8.2));System.out.println("max("+2+"."+"8)=" + Math.max(2,8));System.out.println("min("+2+"."+"8)=" + Math.min(2,8));}
}

字符串类

public class StringD {public static void main(String args[ ]) {String s1 = "Java "; String s2 = "java"; String s3 = "Welcome"; String s4 = "Welcome"; String s5 = "Welcoge"; String sc1 = s3.concat(s1);//sc1的值为"welcome Java"String sc2 = s1.concat("abx"); String str1 = s3.replace('e', 'r'); //s3中的e换成rString w1 = s5.toLowerCase() ;//s5中的字符大写转小写String u2 = s2.toUpperCase();//s2中的字符小写转大写System.out.println("s1=" + s1 + "\t s2=" + s2);System.out.println("s3=" + s3+"\t s4=" + s4);System.out.println("s5=" + s5);System.out.println("s3+s1=" + sc1);System.out.println("s1+abx=" + sc2);System.out.println("s3.replace('e', 'r')= " + str1);System.out.println("s5.toLower=" + w1);System.out.println("s2.toUpper=" + u2);}
}

判断大小写

public class CharacterD {public static void main(String args[ ]) {Character ch = new Character('a'); char c = ch.charValue();if(Character.isUpperCase(c))System.out.println("The character " + c + " is upper case.");else System.out.println("The character" + c + "is lower case.");boolean b = Character.isDigit(c);int x = Character.digit('c',16);System.out.println("b=" + b);System.out.println("x=" + x);}
}

Calendar类的应用范例

import java.util.*;class CalendarD {public static void main(String args[ ]) {Calendar now = Calendar.getInstance();int ampm = now.get(Calendar.AM_PM);int hour = now.get (Calendar.HOUR_OF_DAY);int day = now.get (Calendar.DAY_OF_MONTH);System.out.println(ampm);System.out.println(hour);System.out.println(day);}
}

Random类的范例。随机产生1~6之间的随机整数，统计各数出现的概率

import java.util.*;class RandomDemo {public static void main(String args[ ]) {Random rd = new Random();int[ ] fre = new int[6];int rdGet;for(int i = 0; i <= 100; i ++) {rdGet = Math.abs(rd.nextInt()) % 6 + 1;switch(rdGet) {case 1:fre[0] ++;break;case 2:fre[1] ++;break;case 3:fre[2 ]++;break;case 4:fre[3] ++;break;case 5:fre[4] ++;break;case 6:fre[5] ++;break;}}for(int j = 0; j < fre.length; j ++){System.out.println((j+1) + "出现的次数" + fre[j] + "出现的比率：" + fre[j] / 10.0 + "% ");}
}

一个简单的框架窗口

import javax.swing.*;public class SimpleFrame{public static void main(String args[]){JFrame frame=new JFrame("Simple Frame ");frame.setSize(350,240);frame.setVisible(true);} 
}

通过继承JFrame类实现的窗口（疑惑？）

import javax.swing.*;
public class SimpleFrame extends JFrame{public SimpleFrame(){this("No Title");}public SimpleFrame(String title){super(title);setSize(350,240);setLocation(350,250);setVisible(true);setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);}  }
// SimpleFrameTest.java
public class SimpleFrameTest{public static void main(String args[]){SimpleFrame frame=new SimpleFrame("Simple Frame");}}

向框架窗口中添加按钮组件

import java.awt.Container;
import javax.swing.*;
public class FrameWithButton extends JFrame{JButton jButton1,jButton2;Container cp=null;public FrameWithButton(){this(“No Title”);    }public FrameWithButton(String title){super(title);jButton1 = new JButton(“OK”);jButton2 = new JButton(“Cancel”);cp = getContentPane();cp.add(jButton1);cp.add(jButton2);setSize(400,300);setVisible(true);setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);}   public static void main(String[] args){JFrame frame = new FrameWithButton("Frame With Button");}   
}

BorderLayout的布局的应用

import java.awt.*;
import javax.swing.*;public class BorderDemo extends JFrame {JButton jButton1,jButton2, jButton3,jButton4,jButton5;public BorderDemo() {Container cp = getContentPane();jButton1 = new JButton("North");jButton2 = new JButton("South");jButton3 = new JButton("West");jButton4 = new JButton("East");jButton5 = new JButton("Center");//cp.setLayout(new BorderLayout(10,20));cp.add(jButton1, BorderLayout.NORTH);cp.add(jButton2, BorderLayout.SOUTH);cp.add(jButton3, BorderLayout.WEST);cp.add(jButton4, BorderLayout.EAST);cp.add(jButton5, BorderLayout.CENTER);setSize(400,300);setTitle("BorderLayout Demo");setVisible(true);setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);}public static void main(String args[]) {BorderDemo window = new BorderDemo();   }
}

GridLayout布局的应用

import java.awt.*;
import javax.swing.*;public class GridWindow extends JFrame {public GridWindow() {Container cp = getContentPane();cp.setLayout(new GridLayout(0,2));cp.add(new JButton("Button 1"));cp.add(new JButton("2"));cp.add(new JButton("Button 3"));cp.add(new JButton("Long-Named Button 4"));cp.add(new JButton("Button 5"));}public static void main(String args[]) {GridWindow window = new GridWindow();window.setTitle("GridLayout");window.pack();window.setVisible(true);}
}

向FlowLayout布局的容器中添加多个大小不同的组件

import java.awt.*;
import javax.swing.*;public class FlowWindow extends JFrame {     public FlowWindow() {Container cp = getContentPane();FlowLayout layout = new FlowLayout(FlowLayout.CENTER,10,20);cp.setLayout(layout);cp.add(new JButton("Button 1"));cp.add(new JButton("2"));cp.add(new JButton("Button 3"));cp.add(new JButton("Long-Named Button 4"));cp.add(new JButton("Button 5"));setSize(400,300);setVisible(true);setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);}public static void main(String args[]) {FlowWindow window = new FlowWindow();}
}

通过容器的嵌套实现较复杂的布局

import java.awt.*;
import javax.swing.*;public class FrameWithPanel extends JFrame{JButton btn1,btn2,btn3;Container cp = null;JPanel panel_1,panel_2;public FrameWithPanel(){super("Frame With Panel");btn1 = new JButton("Red");btn2 = new JButton("Green");btn3 = new JButton("Blue");panel_1 = new JPanel();panel_1.setBackground(Color.CYAN);panel_2 = new JPanel();panel_2.setLayout(new FlowLayout(FlowLayout.CENTER,20,10));cp=getContentPane();panel_2.add(btn1);panel_2.add(btn2);panel_2.add(btn3);cp.add(panel_1,BorderLayout.CENTER);cp.add(panel_2,BorderLayout.SOUTH);setSize(300,200);}public static void main(String args[]){FrameWithPanel frame = new FrameWithPanel ();frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame.setVisible(true);}
}

text（you click the button ok）

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;public class EventDemo extends JFrame implements ActionListener{JTextField tf ;JButton btn1,btn2;public EventDemo(){super("Event Demo");tf = new JTextField(20);btn1 = new JButton("OK");btn2 = new JButton("Cancel");container cp = getContentPane();cp.setLayout(new FlowLayout());cp.add(tf);cp.add(btn1);cp.add(btn2);btn1.addActionListener(this);btn2.addActionListener(this);}public void actionPerformed(ActionEvent e){if((JButton)e.getSource()==btn1)tf.setText("you clicked button OK");else if((JButton)e.getSource()==btn2)tf.setText("you clicked button Cancel");}public static void main(String[]args){EventDemo frame = new EventDemo();frame.setSize(400,100);frame.setLocation(200,200);frame.setVisible(true);frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);}
}

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