从零自学Java-3.在程序中存储和修改变量信息

1.创建变量；

2.使用不同类型的变量；

3.在变量中存储值；

4.在数学表达式中使用变量；

5.把一个变量的值赋给另一个变量；

6.递增/递减变量的值。

程序Variable：使用不同类型的变量并赋初值

 package com.jsample;

 public class Variable {
     public static void main(String[] args){
         int tops;//无初值的整型变量
         float gpa;//无初值的单精度浮点型变量
         char key = 'C';//初值为‘C’的字符型变量
         String productName = "Larvets";//初值为“Larvets”的字符串型变量
     }//本程序无输出
 }

程序PlaneWeight：计算并输出人在太阳系不同行星上的体重值

 package com.jsample;

 public class PlaneWeight {
     public static void main(String[] args){
         System.out.print("Your weight on Earth is ");
         double weight = 178;
         System.out.println(weight);//print()不会自动换行，println()会

         System.out.print("Your weight on Mercury is ");
         double mercury = 178 * .378;
         System.out.println(mercury);

         System.out.print("Your weight on Moon is ");
         double moon = 178 * .166;
         System.out.println(moon);

         System.out.print("Your weight on Jupiter is ");
         double jupiter = 178 * 2.364;
         System.out.println(jupiter);
     }
 }

程序PlaneWeightPlus：计算并输出人在更多太阳系不同行星上的体重值

 package com.jsample;

 public class PlaneWeightPlus {
     public static void main(String[] args){
         System.out.print("Your weight on Earth is ");
         double weight = 178;
         System.out.println(weight);//print()不会自动换行，println()会

         System.out.print("Your weight on Mercury is ");
         double mercury = weight * .378;
         System.out.println(mercury);

         System.out.print("Your weight on Moon is ");
         double moon = weight * .166;
         System.out.println(moon);

         System.out.print("Your weight on Jupiter is ");
         double jupiter = weight * 2.364;
         System.out.println(jupiter);

         System.out.print("Your weight on Hesperus is ");
         double hesperus = weight * .907;
         System.out.println(hesperus);

         System.out.print("Your weight on Uranus is ");
         double uranus = weight * .889;
         System.out.println(uranus);
     }
 }

程序SquareSum：计算整型数x,y的平方和并输出

 package com.jsample;

 public class SquareSum {
     public static void main(String[] args){
         int x = 1;
         int y = 1;
         System.out.println(x * x + y * y);//输出平方和
     }
 }