zh:courses:java2025:ch02
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zh:courses:java2025:ch02 [2025/02/16 10:53] pzczxs [上机作业] |
zh:courses:java2025:ch02 [2025/04/04 11:26] (当前版本) pzczxs 讨论状态变化了 |
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| 行 93: | 行 93: | ||
| ===== 程序控制流：if ===== | ===== 程序控制流：if ===== | ||
| - | java.util.Random类的方法nextInt()产生随机整数，生成两个随机整数，用if-else 语句找出其中的较小者 | + | java.util.Random类的方法nextInt()产生随机整数，生成两个随机整数，用if-else 语句找出较小者 |
| <file java IfElse.java> | <file java IfElse.java> | ||
| 行 248: | 行 248: | ||
| int n = 0, m, j, i; | int n = 0, m, j, i; | ||
| System.out.print("2"); | System.out.print("2"); | ||
| - | p1: for (i = 3; i <= 100; i += 2) { | + | label: for (i = 3; i <= 100; i += 2) { |
| m = (int) Math.sqrt((double) i); | m = (int) Math.sqrt((double) i); | ||
| for (j = 2; j <= m; j++) { | for (j = 2; j <= m; j++) { | ||
| 行 255: | 行 255: | ||
| } | } | ||
| if (i == 51) { | if (i == 51) { | ||
| - | break p1; | + | break label; |
| } | } | ||
| } | } | ||
| 行 276: | 行 276: | ||
| public class ContinueExample { | public class ContinueExample { | ||
| public static void main(String[] args) { | public static void main(String[] args) { | ||
| - | outer: for (int i = 0; i < 2; i++) { | + | label: for (int i = 0; i < 2; i++) { |
| System.out.println("运行第一重循环" + i); | System.out.println("运行第一重循环" + i); | ||
| for (int j = 0; j < 2; j++) { | for (int j = 0; j < 2; j++) { | ||
| 行 285: | 行 285: | ||
| if (k == 1) { | if (k == 1) { | ||
| System.out.println("跳出多重循环"); | System.out.println("跳出多重循环"); | ||
| - | continue outer; | + | continue label; |
| } | } | ||
| 行 298: | 行 298: | ||
| ===== 上机作业 ===== | ===== 上机作业 ===== | ||
| - | * 习题3.11：编写程序，求$1 + 3 + 7 + 15 + 31 + \cdots + (2^{20} - 1)$的值； | + | * 编写程序，求$1 + 3 + 7 + 15 + 31 + \cdots + (2^{20} - 1)$的值； |
| - | * 习题3.12：已知$S = 1 - \frac{1}{2} + \frac{1}{3} - \frac{1}{4} + \cdots + \frac{1}{n - 1} - \frac{1}{n}$，试编写程序求解直到满足$\frac{1}{n} < {10}^{-5}$时的$S$值； | + | 【参考答案】 |
| + | <file java TowPowSummation.java> | ||
| + | package cn.edu.bjut.chapter2; | ||
| + | |||
| + | public class TwoPowerSummation { | ||
| + | public static void main(String[] args) { | ||
| + | int sum = 0; | ||
| + | for (int n = 1; n <= 20; n++) { | ||
| + | sum += (int) Math.pow(2, n) - 1; | ||
| + | } | ||
| + | |||
| + | System.out.println(sum); | ||
| + | } | ||
| + | } | ||
| + | </file> | ||
| + | * 已知$S = 1 - \frac{1}{2} + \frac{1}{3} - \frac{1}{4} + \cdots + \frac{1}{n - 1} - \frac{1}{n}$，试编写程序求解直到满足$\frac{1}{n} < {10}^{-5}$时的$S$值； | ||
| + | 【参考答案】 | ||
| + | <file java FractionSummation.java> | ||
| + | package cn.edu.bjut.chapter2; | ||
| + | |||
| + | public class FractionSummation { | ||
| + | public static void main(String[] args) { | ||
| + | double sum = 0; | ||
| + | for (int n = 1; (1.0 / n >= 1e-5); n++) { | ||
| + | if (n % 2 == 0) { // 偶数 | ||
| + | sum -= 1.0 / n; | ||
| + | } else { // 奇数 | ||
| + | sum += 1.0 / n; | ||
| + | } | ||
| + | } | ||
| + | System.out.println(sum); | ||
| + | } | ||
| + | } | ||
| + | </file> | ||
| * 编写程序，计算没有数码9的三位数有多少个，它们的和等于多少？ | * 编写程序，计算没有数码9的三位数有多少个，它们的和等于多少？ | ||
| + | 【参考答案】 | ||
| + | <file java ThreeDigitNumber.java> | ||
| + | package cn.edu.bjut.chapter2; | ||
| + | |||
| + | public class ThreeDigitNumber { | ||
| + | public static void main(String[] args) { | ||
| + | int count = 0; | ||
| + | int sum = 0; | ||
| + | |||
| + | for (int i = 100; i < 1000; i++) { | ||
| + | String str = String.valueOf(i); | ||
| + | if (str.indexOf('9') >= 0) { | ||
| + | continue; | ||
| + | } | ||
| + | |||
| + | count++; | ||
| + | sum += i; | ||
| + | } | ||
| + | |||
| + | System.out.println(count + "\t" + sum); | ||
| + | } | ||
| + | } | ||
| + | </file> | ||
| * 国际专利分类号（IPC）的前15位由section（部），class（大类），subclass（小类），main group（大组）和sub group（小组）五部分组成，每位的要求如下表所示，具体例子如：“G06F 17/30”和“H01M 10/587”，编写程序将这五部分拼接成IPC的实际表现形式； | * 国际专利分类号（IPC）的前15位由section（部），class（大类），subclass（小类），main group（大组）和sub group（小组）五部分组成，每位的要求如下表所示，具体例子如：“G06F 17/30”和“H01M 10/587”，编写程序将这五部分拼接成IPC的实际表现形式； | ||
| 行 311: | 行 367: | ||
| | 10-14 | subgroup（左对齐） | 0...99999 | | | 10-14 | subgroup（左对齐） | 0...99999 | | ||
| + | 【参考答案】 | ||
| + | <file java Ipc.java> | ||
| + | package cn.edu.bjut.chapter2; | ||
| + | |||
| + | public class Ipc { | ||
| + | public static void main(String[] args) { | ||
| + | final char SEPARATOR = '/'; | ||
| + | |||
| + | { | ||
| + | char section = 'A'; | ||
| + | int mainClass = 4; | ||
| + | char subclass = 'B'; | ||
| + | int mainGroup = 55; | ||
| + | int subgroup = 56; | ||
| + | |||
| + | String classification = section | ||
| + | + String.format("%2s", mainClass).replace(' ', '0') | ||
| + | + subclass + String.format("%4s", mainGroup) | ||
| + | + SEPARATOR + subgroup; | ||
| + | |||
| + | System.out.println(classification); | ||
| + | } | ||
| + | |||
| + | { | ||
| + | String classification = "A04B 55/56"; | ||
| + | char section = classification.charAt(0); | ||
| + | int mainClass = Integer.parseInt(classification.substring(1, 3)); | ||
| + | char subclass = classification.charAt(3); | ||
| + | int pos = classification.indexOf(SEPARATOR); | ||
| + | int mainGroup = Integer.parseInt(classification.substring(4, pos).trim()); | ||
| + | int subgroup = Integer.parseInt(classification.substring(pos + 1)); | ||
| + | |||
| + | System.out.println(section + "\t" + mainClass + "\t" | ||
| + | + subclass + "\t" + mainGroup + "\t" | ||
| + | + subgroup); | ||
| + | } | ||
| + | } | ||
| + | } | ||
| + | </file> | ||
| [[zh:courses:java2025:index|返回Java课程页]] | [[zh:courses:java2025:index|返回Java课程页]] | ||
| - | ~~DISCUSSION~~ | + | ~~DISCUSSION:closed~~ |
zh/courses/java2025/ch02.1739674395.txt.gz · 最后更改: 2025/02/16 10:53 由 pzczxs