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class Student{ |
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String studentId; |
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String name; |
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double score; |
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//define a study approach |
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void study() { |
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System.out.println(studentId+" "+name+"正在学习,上一次的成绩是"+score); |
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} |
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} |
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public class Main { |
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public static void main (String[] args) { |
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//setting up the first object |
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Student s1=new Student(); |
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s1.studentId="001"; |
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s1.name="George"; |
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s1.score=90; |
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//setting up the second object |
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Student s2=new Student(); |
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s2.studentId="002"; |
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s2.name="Roya"; |
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s2.score=95; |
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//using the approach study() |
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s1.study(); |
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s2.study(); |
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} |
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} |
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1. 为什么需要显式数据类型声明? |
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因为Java是编译型语言,需要提前知道数据类型来分配内存和检查类型错误。 |
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编译时必须确定每个变量占用多少内存(如int占4字节,double占8字节) |
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编译时检查类型是否匹配,防止运行时才崩溃(如不能把字符串当数字计算) |
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2.为什么需要public这类访问修饰符? |
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因为Java需要明确控制谁能访问什么,保证程序安全性和结构清晰。 |
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public:任何人都能访问(如main方法必须public,因为JVM要从外部调用) |
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private:只有自己能用(隐藏内部细节,防止乱改数据) |
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不写(默认):同一包内能用 |
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protected:子类能用 |
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@ -0,0 +1,2 @@ |
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python就像自波车 只有油门和刹车 简单易操作 但是遇到紧急情况容易把油门当刹车踩 并且更耗油 |
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java就像手波车 除了油门刹车 还有一个离合器 操作较繁琐 但是遇到危险可以直接踩下离合器切断汽车动力 比较安全 并且手动控制档位 更省油 |
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@ -0,0 +1,55 @@ |
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import java.util.Scanner; |
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public class TemperatureConverter { |
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// 将摄氏度转换为华氏度 |
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public static double celsiusToFahrenheit(double c) { |
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return c * 9.0 / 5.0 + 32.0; |
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} |
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// 将华氏度转换为摄氏度 |
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public static double fahrenheitToCelsius(double f) { |
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return (f - 32.0) * 5.0 / 9.0; |
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} |
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public static void main(String[] args) { |
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Scanner scanner = new Scanner(System.in); |
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System.out.print("请输入要转换的温度与单位(例如 36.6 C 或 97 F):"); |
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String input = scanner.nextLine().trim(); |
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if (input.isEmpty()) { |
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System.out.println("输入为空,程序退出。"); |
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scanner.close(); |
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return; |
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} |
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String[] parts = input.split(" "); |
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double value; |
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String unit; |
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try { |
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value = Double.parseDouble(parts[0]); |
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if (parts.length > 1) { |
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unit = parts[1].toUpperCase(); |
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} else { |
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unit = "C"; |
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} |
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} catch (Exception e) { |
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System.out.println("输入解析失败,请按示例输入数值与单位,例如:36.6 C"); |
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scanner.close(); |
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return; |
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} |
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if (unit.startsWith("C")) { |
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double f = celsiusToFahrenheit(value); |
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System.out.printf("%.2f °C = %.2f °F%n", value, f); |
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} else if (unit.startsWith("F")) { |
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double c = fahrenheitToCelsius(value); |
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System.out.printf("%.2f °F = %.2f °C%n", value, c); |
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} else { |
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System.out.println("未知单位,请使用 C 或 F。"); |
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} |
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scanner.close(); |
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} |
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} |
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