Java常用实用类（分两次更）

p220

1．public class E {
  public static void main (String args[ ]) {
     String s1,s2,t1="ABCDabcd";
     s1=t1.toUpperCase();
     s2=t1.toLowerCase(); 
     System.out.println(s1);
     System.out.println(s2);
     String s3=s1.concat(s2);
      System.out.println(s3);
   }
}
2.   public class E {
  public static void main (String args[ ]) {
     String s="ABCDabcd";
     char cStart=s.charAt(0);
     char cEnd = s.charAt(s.length()-1);
     System.out.println(cStart);
     System.out.println(cEnd);
   }
}
3.   import java.util.*;
public class E {
  public static void main (String args[ ]) {
    int year1,month1,day1,year2,month2,day2;
      try{ year1=Integer.parseInt(args[0]);
           month1=Integer.parseInt(args[1]);
           day1=Integer.parseInt(args[2]);
           year2=Integer.parseInt(args[3]);
           month2=Integer.parseInt(args[4]);
           day2=Integer.parseInt(args[5]);
       }
       catch(NumberFormatException e)
         { year1=2012;
           month1=0;
           day1=1;
           year2=2018;
           month2=0;
           day2=1;
       } 
       Calendar calendar=Calendar.getInstance(); 
       calendar.set(year1,month1-1,day1);  
       long timeYear1=calendar.getTimeInMillis();
       calendar.set(year2,month2-1,day2);  
       long timeYear2=calendar.getTimeInMillis();
       long 相隔天数=Math.abs((timeYear1-timeYear2)/(1000*60*60*24));
       System.out.println(""+year1+"年"+month1+"月"+day1+"日和"+
                            year2+"年"+month2+"月"+day2+"日相隔"+相隔天数+"天");
   }
}
4.   import java.util.*;
public class E {
  public static void main (String args[ ]) {
   double a=0,b=0,c=0;
      a=12;
      b=24;
      c=Math.asin(0.56);
      System.out.println(c);
      c=Math.cos(3.14);
      System.out.println(c);
      c=Math.exp(1);
      System.out.println(c);
      c=Math.log(8);
      System.out.println(c);
   }
}
5．public class E {
      public static void main (String args[ ]) {
        String str = "ab123you你是谁？";
        String regex = "\\D+";
        str = str.replaceAll(regex,"");
        System.out.println(str);
      }
}
6． import java.util.*;
public class E {
   public static void main(String args[]) {
      String cost = "数学87分，物理76分，英语96分";
      Scanner scanner = new Scanner(cost);
      scanner.useDelimiter("[^0123456789.]+");
      double sum=0;
      int count =0;
      while(scanner.hasNext()){
         try{  double score = scanner.nextDouble();
               count++;
               sum = sum+score;
               System.out.println(score);
         } 
         catch(InputMismatchException exp){
              String t = scanner.next();
         }   
      }
      System.out.println("总分:"+sum+"分");
      System.out.println("平均分:"+sum/count+"分");
   }
}