通过实例可以更好的了解java

3-例子1
public class Example1_1
{ 
  public static void main(String args[])
  {
     int math=65 ,english=85;
     if(math>60)
       { System.out.println("数学及格了"); }
     else
       { System.out.println("数学不及格"); }
     if(english>90)
       { System.out.println("英语是优");}
     else
       { System.out.println("英语不是优");}
     if(math>60&&english>90)
       { System.out.println("英语是优,数学也及格了");}
     else
      {  }
     System.out.println("我在学习控制语句");
  }
}


3-例子2
import java.applet.*;
import java.awt.*;
public class Example1_2 extends Applet
{
  public void paint(Graphics g)
  { int x=2,y=1;
    switch(x+y)
    { 
     case 1 :
        g.setColor(Color.red);
        g.drawString("i am 1",5,10);
        break;    
     case 2:
        g.setColor(Color.blue);
        g.drawString("i am 2",5,10);
        break;   
     case 3:   
        g.setColor(Color.green);
        g.drawString("i am 3",5,10);
        break;     
     default:
        g.drawString("没有般配的",5,10);
    }
  }
}  


3-例子3 
求从1加到100的和 
import java.applet.*;
import java.awt.*;
public class Example1_3  extends Applet
{
  public void paint(Graphics g)
  {  int sum=0; 
    for(int i=1;i<=100;i++)
       { 
         sum=sum+i;
       }
   g.drawString("sum= "+sum,10,20);
  }
}


3-例子4  
求10的阶乘 
import java.applet.*;
import java.awt.*;
public class Example1_4  extends Applet
{
  public void paint(Graphics g)
  {  long jiecheng=1; 
    for(int i=10;i>=1;i--)
       { 
         jiecheng=jiecheng*i;
       }
   g.drawString("10的阶乘是 "+jiecheng,10,20);
  }
}


3-例子5
import java.applet.*;
import java.awt.*;
public class Example1_5 extends Applet
 { int sum=0,i=1;
  public void paint(Graphics g)
  {    while(i<=100)
     { sum=sum+i;i++;}
   g.drawString("sum=  "+sum,10,10);
  }
}


3-例子 6
class Example1_6
{public static void main(String args[])
  { int sum=0,i,j;
     for( i=1;i<=10;i++) 
       { if(i%2==0) continue;//计算1+3+5+7+9
         else {}  
         sum=sum+i;
       }
     System.out.println("sum="+sum);
     for( j=2;j<=50;j++)    //求50以内的素数
      {for( i=2;i<=j/2;i++)
        {if(j%i==0) break;
        }
       if(i>j/2)
        {System.out.println(""+j+"是素数");}
       else
         {}
      }      
   }
}


3-例子7

package tom.jiafei;
public class  PrimNumber
{ public static void main(String args[])
  { int sum=0,i,j;
     for( i=1;i<=100;i++)  //找出100以内的素数。
       {for(j=2;j<=i/2;j++)
          {if(i%j==0)
             break;
          }
        if(j>i/2) System.out.println("素数："+i);       
       }
  }
}


3-例子8.
import java.applet.Applet;
import java.awt.*;
public class Example1_8 extends Applet 
{ Button redbutton;
  public void init()
{ redbutton=new Button("ok"); redbutton.setBackground(Color.red);
  add(redbutton);
     }
public void  paint(Graphics g)
    { g.drawString("it is a button",30,50);
    }
}


3-例子9
import tom.jiafei.*; //引入自己的包。
public class TestPack
{public static void main(String args[])
  {PrimNumber num=new PrimNumber();//用包tom.jiafei中的类创建对象。
   String a[]={"ok"};
    System.out.println(a[0]);
    num.main(a);
  }
}


3-例子10
import PrimNumber
public class TestPack
{public static void main(String args[])
  {PrimNumber num=new PrimNumber();//要保证PrimNuber类和TestPack类在同
//一目录中。
   String a[]={"ok"};
    System.out.println(a[0]);
    num.main(a);
  }
}