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
    }
}