语源科技BlogJava-天涯若比邻

java2从头开学（13）

dripstone — Fri, 11 Apr 2008 06:35:00 GMT

package 数据类型;
//作用域
class Scope {
public static void main(String args[]){
  int x;

  x = 10;
  if(x == 10){
   int y = 20;

   System.out.println("x and y: " + x + " " + y);
   x = y * 2;
  }
  // y = 100;//Error! y not known here

  // x is still known here.
  System.out.println("x is " + x);
}

}

dripstone 2008-04-11 14:35 发表评论

java2从头开学（12）

dripstone — Fri, 11 Apr 2008 06:35:00 GMT

package 数据类型;
//类型提升约定
class Promote {
public static void main(String args[]){
  byte b = 42;
  char c = 'a';
  short s = 1024;
  int i = 50000;
  float f = 5.67f;
  double d = .1234;
  double result = (f * b) + (i / c) - (d * s);
  System.out.println((f * b) + " + " + (i / c) + " - " + (d * s));
  System.out.println("result = " + result);
}
}

dripstone 2008-04-11 14:35 发表评论

java2从头开学（11）

dripstone — Fri, 11 Apr 2008 06:34:00 GMT

package 数据类型;

//长整型
class Light {
public static void main(String args[]){
  int lightspeed;
  long days;
  long seconds;
  long distance;

  lightspeed = 186000;

  days = 1000;

  seconds = days*24*60*60;

  distance = lightspeed*seconds;

  System.out.print("输入" + days);
  System.out.print("光在这些天内将旅行");
  System.out.println(distance + "米。");
}

}

dripstone 2008-04-11 14:34 发表评论

java2从头开学（10）

dripstone — Fri, 11 Apr 2008 06:34:00 GMT

package 数据类型;
//如果一个声明定义包含一个初始化，那么每次进入声明它的程序块时，该变量都要被重新初始化
class LifeTime {
public static void main(String args[]){
  int x;

  for(x = 0; x < 3; x++){
   int y = -1;
   System.out.println("y is: " + y);
   y = 100;
   System.out.println("y is now: " + y);
  }
}

}

dripstone 2008-04-11 14:34 发表评论

java2从头开学（9）

dripstone — Fri, 11 Apr 2008 06:34:00 GMT

package 数据类型;
//动态初始化
class DynInit {
public static void main(String args[]){
  double a = 3.0, b = 4.0;

  double c = Math.sqrt(a * a + b * b);//sqrt()为Java的内置方法，求参数的平方根

  System.out.println("斜边长度为 " + c);
}

}

dripstone 2008-04-11 14:34 发表评论

java2从头开学（8）

dripstone — Fri, 11 Apr 2008 06:33:00 GMT

package 数据类型;
//强制类型转换
class Conversion {
public static void main(String args[]){
  byte b;
  int i = 257;
  double d = 323.142;

  System.out.println("\nConversion of int to byte.");
  b = (byte) i;
  System.out.println("i and b " + i + " " + b);

  System.out.println("\nConversion of double to byte.");
  i = (int) d;
  System.out.println("d and i " + d + " " + i);

  System.out.println("\nConversion of double to byte.");
  b = (byte) d;
  System.out.println("d and b " + d + " " + b);
}

}

dripstone 2008-04-11 14:33 发表评论

java2从头开学（7）

dripstone — Fri, 11 Apr 2008 06:33:00 GMT

package 数据类型;
//字符相加char
class CharDemo2 {
public static void main(String args[]){
  char ch1;

  ch1 = 'X';
  System.out.println("ch1 contains " + ch1);
  ch1++;
  System.out.println("ch1 is now " + ch1);
}
}
/*
* ch1首先被赋值X。然后变量ch1递增（自增量1）
* 结果ch1带表Y
* 即在ASCII（以及Unicode）字符集中的下一个字符
*/

dripstone 2008-04-11 14:33 发表评论

java2从头开学（6）

dripstone — Fri, 11 Apr 2008 06:32:00 GMT

package 数据类型;
//char变量
class CharDemo {
public static void main(String args[]){
  char ch1,ch2;

  ch1 = 88;//88是ASCII码（Unicode码也一样）用来代表字母X
  ch2 = 'Y';

  System.out.print("ch1和ch2：");
  System.out.println(ch1 + "" + ch2);
}

}

dripstone 2008-04-11 14:32 发表评论

java2从头开学（5）

dripstone — Fri, 11 Apr 2008 06:32:00 GMT

package 数据类型;
//布尔类型
class BoolTest {
public static void main(String args[]){
  boolean b;

  b = false;
  System.out.println("b is " + b);
  b = true;
  System.out.println("b is " + b);//布尔型显示为true和false

  if(b) System.out.println("this is not executed.");//布尔本身可以空if语句，不用写成if(b == true)
  System.out.println("10 > 9 is " + (10>9));// > 符号返回类型为布尔型
}

}

dripstone 2008-04-11 14:32 发表评论

java2从头开学（4）

dripstone — Fri, 11 Apr 2008 06:31:00 GMT

package 数据类型;
//运用一维数组计算一组数字的平均数
class Average {
public static void main(String args[]){
  double nums[] = {10.1,11.2,12.3,13.4,14.5};
  double result = 0;
  int i;

  for(i=0; i<5; i++)
   result = result + nums[i];
  System.out.println("Average is " + result / 5);
}

}

dripstone 2008-04-11 14:31 发表评论