zh:courses:java2026:ch02
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zh:courses:java2026:ch02 [2026/02/22 17:45] pzczxs 创建 |
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| ====== 第二章：Java语言基础 ====== | ====== 第二章：Java语言基础 ====== | ||
| ===== 课件 ===== | ===== 课件 ===== | ||
| - | 下载：Java语言基础 | + | 下载：{{ :zh:courses:java2026:ch02.pptx |Java语言基础}} |
| ===== 整型数据测试程序 ===== | ===== 整型数据测试程序 ===== | ||
| 行 299: | 行 299: | ||
| ===== 上机作业 ===== | ===== 上机作业 ===== | ||
| * 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； | ||
| - | 【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； | * 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 366: | 行 310: | ||
| | 9 | 分割符 | / | | | 9 | 分割符 | / | | ||
| | 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:java2026:index|返回Java课程页]] | [[zh:courses:java2026:index|返回Java课程页]] | ||
| ~~DISCUSSION~~ | ~~DISCUSSION~~ | ||
zh/courses/java2026/ch02.1771753539.txt.gz · 最后更改: 2026/02/22 17:45 由 pzczxs