public class Demo { public static void main(String[] args) { Scanner sc = new Scanner(System.in); String s = sc.nextLine(); Map<Character, Integer> m = new HashMap<>(); for (int i = 0; i < s.length() - 1; i++) { char c = s.charAt(i); if (m.get(c) != null) { int value = m.get(c); m.put(c, (value + 1)); } else { m.put(c, 1); } } Set<Map.Entry<Character,Integer>> entries=m.entrySet(); for(Map.Entry<Character,Integer> map1:entries){ System.out.println(map1.getKey()+"出现了"+map1.getValue()+"次"); } } }这个代码有什么问题
时间: 2024-02-14 16:16:27 浏览: 36
这段代码有个潜在的问题就是只遍历了字符串中的前s.length()-1个字符,因此会漏掉最后一个字符。应该将for循环的条件改为 i < s.length():
```
for (int i = 0; i < s.length(); i++) {
// ...
}
```
此外,代码中没有对输入的字符串进行空指针判断,如果输入的字符串为null,将会抛出NullPointerException异常。可以在读取输入时进行判断:
```
String s = sc.nextLine();
if (s == null) {
// 处理空输入的情况
}
```
相关问题
import java.io.*; import java.util.*; import java.util.Scanner; public class demo{ public static void main(String[] args){ Scanner sc=new Scanner(System.in); int a=sc.nextInt(); //a是要输入的字符 for(int i=1;i<7;i+=2){ for(int j=1;j<=(7-i)/2;j++){ System.out.print(" "); } for(int j=1;j<=i;j++){ System.out.print(a); } System.out.println(); } } }解释代码
这段代码是一个简单的Java程序,用于打印出一个带有空格的字符图案。下面对代码进行解释:
1. `import java.io.*;` 和 `import java.util.*;` 这两行代码导入了Java的输入输出和工具类库。
2. `import java.util.Scanner;` 这行代码导入了Scanner类,用于接收用户的输入。
3. `public class demo { ... }` 这是定义了一个名为demo的公共类。
4. `public static void main(String[] args) { ... }` 这是定义了一个名为main的公共静态方法,是程序的入口点。
5. `Scanner sc = new Scanner(System.in);` 这行代码创建了一个Scanner对象sc,用于接收从标准输入读取的数据。
6. `int a = sc.nextInt();` 这行代码使用nextInt()方法从用户输入中读取一个整数,并将其赋值给变量a。
7. `for(int i = 1; i < 7; i += 2) { ... }` 这是一个外层循环,用于控制字符图案的行数。循环条件是i小于7,并且每次循环加2。
8. `for(int j = 1; j <= (7 - i) / 2; j++) { ... }` 这是一个内层循环,用于打印每行的空格。循环次数是(7 - i) / 2,即每行前面的空格数。
9. `System.out.print(" ");` 这行代码打印一个空格。
10. `for(int j = 1; j <= i; j++) { ... }` 这是另一个内层循环,用于打印每行的字符。循环次数是i,即每行的字符数。
11. `System.out.print(a);` 这行代码打印字符a。
12. `System.out.println();` 这行代码打印一个换行符,用于换行。
这样,根据用户输入的整数a,程序将打印出一个带有空格的字符图案。图案的行数为6,每行字符的数量依次为1、3、5、7、9、11,字符为用户输入的整数a。
package demo; import java.util.HashMap; import java.util.Scanner; public class exercise333 { private static Scanner scanner; /** * 学生信息集合 */ private static HashMap<String,Student> map; public static void main(String[] args) { // TODO Auto-generated method stub select(); } private static void select() { System.out.println("请输入学号:"); Scanner sc = new Scanner(System.in); String nub = sc.nextLine(); Student student = map.get(nub); if(student == null) System.out.println("没有查询到该学生!"); else System.out.println(student.toString()); } } class Student{ private String sno; /** * 学号 */ private String name; /** * 姓名 */ private String major; /** * 专业 */ private String score; /** * 成绩 */ public String toString() { return "学生信息{"+ "学号='" + sno + '\'' + "姓名='" + name + '\'' + "专业='" + major + '\'' + "成绩='" + score + '\'' + '}'; } public String getSno() { return sno; } public void setSno(String sno) { this.sno = sno; } public String getName() { return name ; } public void setName(String name) { this.name = name; } public String getMajor() { return major; } public void setMajor(String major) { this.major = major; } public String getScore() { return score; } public void setScore(String score) { this.score =score; } public Student(String sno,String name,String major,String score) { this.sno = sno; this.name = name; this.major = major; this.score = score; } }
There are a few issues with the provided code:
1. The `map` object is not initialized, which will cause a `NullPointerException` when using the `get` method. To fix this, initialize the map object before using it:
```
private static HashMap<String,Student> map = new HashMap<String,Student>();
```
2. The `toString` method in the `Student` class is missing some plus signs to concatenate the strings. Fix it by adding the plus signs:
```
public String toString() {
return "学生信息{" +
"学号='" + sno + '\'' +
", 姓名='" + name + '\'' +
", 专业='" + major + '\'' +
", 成绩='" + score + '\'' +
'}';
}
```
3. The `score` field is declared as `String`, which is not a suitable type for storing scores. Change it to a numeric type, such as `int` or `double`.
4. The `setScore` method has a typo and should be `this.score = score;`
5. It's a good practice to use `try-catch` blocks when reading from input, as the input could be incorrect and cause exceptions. For example, using `Integer.parseInt()` to get an integer from input could throw a `NumberFormatException`, and using `scanner.nextLine()` could throw a `NoSuchElementException` if there is no more input available.
Here is the fixed code with these issues addressed:
```
package demo;
import java.util.HashMap;
import java.util.Scanner;
public class Exercise333 {
private static Scanner scanner;
/** 学生信息集合 */
private static HashMap<String, Student> map = new HashMap<String, Student>();
public static void main(String[] args) {
// TODO Auto-generated method stub
select();
}
private static void select() {
System.out.println("请输入学号:");
Scanner sc = new Scanner(System.in);
String nub = sc.nextLine();
try {
Student student = map.get(nub);
if (student == null)
System.out.println("没有查询到该学生!");
else
System.out.println(student.toString());
} catch (Exception e) {
System.out.println("输入有误!");
} finally {
sc.close();
}
}
}
class Student {
private String sno; /** 学号 */
private String name; /** 姓名 */
private String major; /** 专业 */
private int score; /** 成绩 */
public String toString() {
return "学生信息{" +
"学号='" + sno + '\'' +
", 姓名='" + name + '\'' +
", 专业='" + major + '\'' +
", 成绩='" + score + '\'' +
'}';
}
public String getSno() {
return sno;
}
public void setSno(String sno) {
this.sno = sno;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getMajor() {
return major;
}
public void setMajor(String major) {
this.major = major;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
public Student(String sno, String name, String major, int score) {
this.sno = sno;
this.name = name;
this.major = major;
this.score = score;
}
}
```
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