string rs = sb2.tostring();
时间: 2023-09-19 10:03:16 浏览: 32
在这段代码中,rs是一个字符串变量,它的值是通过调用sb2对象的tostring()方法得到的。tostring()方法是将sb2对象转换为字符串表示形式的方法。
StringBuilder类(sb2)是Java语言中的一个可变字符串类,它允许进行更高效的字符串操作。当我们需要频繁修改字符串时,使用StringBuilder类比直接使用String类更加高效。
tostring()是StringBuilder类中定义的一个方法,用于将StringBuilder对象转换为字符串。它会返回一个包含StringBuilder对象中字符序列的不可变的字符串对象。这样我们就能够更方便地在程序中使用StringBuilder对象的字符串表示形式进行操作和处理。
因此,在这段代码中,当我们调用sb2对象的tostring()方法,它会返回一个字符串表示sb2对象的不可变字符串对象,并将该对象的引用赋给rs变量。这样我们就可以通过rs变量来获取和使用sb2对象的字符串表示形式,以便于后续的操作和处理。
相关问题
public static GPA PersonalReader()throws IOException{ // Read credit information from a JSON file String file = "C:\\Users\\isabe\\Desktop\\code\\code\\src\\STUDENT\\1001.json"; try{ FileReader fileReader = new FileReader(file); Reader reader = new InputStreamReader(new FileInputStream(file),"Utf-8"); int ch = 0; StringBuffer sb = new StringBuffer(); while ((ch = reader.read()) != -1) { sb.append((char) ch); } reader.close(); fileReader.close(); File file1 = new File("C:\\Users\\isabe\\Desktop\\code\\code\\src\\credit.json"); FileReader fileReader1 = new FileReader(file1); Reader reader1 = new InputStreamReader(new FileInputStream(file1), "Utf-8"); int ch1 = 0; StringBuffer sb2 = new StringBuffer(); while ((ch1 = reader1.read()) != -1) { sb2.append((char) ch1); } fileReader1.close(); reader1.close(); String creditStr = sb2.toString(); // Parse JSON strings using FastJSON library and calculate weighted GPA JSONObject jsonObject2 = JSON.parseObject(creditStr); double weighteGpa = 0.0; double Cre = 0.0; String jsonStr = sb.toString(); JSONObject jsonObject = JSON.parseObject(jsonStr); JSONArray subjectsList = jsonObject.getJSONArray("subjectsList"); Double avgGrade = 0.0; for (int i = 0; i < subjectsList.size(); i++) { JSONObject subject = subjectsList.getJSONObject(i); String subjectName = subject.getString("subject"); JSONObject jsonObject1 = jsonObject2.getJSONObject(subjectName); Object o = jsonObject1.getDouble("credit"); Double grade = subject.getDouble("grade"); weighteGpa += Double.parseDouble(o.toString())*grade; Cre += Double.parseDouble(o.toString()); avgGrade += grade; } avgGrade = avgGrade / subjectsList.size(); System.out.println(avgGrade); // Return GPA object return new GPA(avgGrade+"",(weighteGpa/(10*Cre)-5)+""); } catch (IOException e) { e.printStackTrace(); return null; } }使用tdd修改这段代码
首先,需要为该方法编写测试用例。我们可以编写以下几个测试用例:
1. 当文件路径存在且文件内容正确时,应正确计算加权平均GPA并返回GPA对象。
2. 当文件路径存在但文件内容格式不正确时,应该返回null。
3. 当文件路径不存在时,应该抛出FileNotFoundException异常。
针对这些测试用例,我们可以先编写测试代码:
```
@Test
public void testPersonalReader() throws IOException {
// Test case 1: file path exists and file content is correct
String file = "C:\\Users\\isabe\\Desktop\\code\\code\\src\\STUDENT\\1001.json";
GPA result1 = PersonalReader(file);
assertEquals("3.7", result1.getGPA());
assertEquals("3.0", result1.getWeightedGPA());
// Test case 2: file path exists but file content is incorrect
String file2 = "C:\\Users\\isabe\\Desktop\\code\\code\\src\\STUDENT\\1002.json";
GPA result2 = PersonalReader(file2);
assertNull(result2);
// Test case 3: file path does not exist
String file3 = "C:\\Users\\isabe\\Desktop\\code\\code\\src\\STUDENT\\1003.json";
assertThrows(FileNotFoundException.class, () -> {
PersonalReader(file3);
});
}
```
接下来,我们需要根据测试用例来修改代码。首先,需要将原方法的方法名和参数修改为符合TDD的方式:
```
public static GPA PersonalReader(String file) throws IOException {
// ...
}
```
然后,在方法中增加如下代码:
```
File f = new File(file);
if (!f.exists()) {
throw new FileNotFoundException("File not found: " + file);
}
```
这段代码用于判断文件是否存在,如果不存在则抛出FileNotFoundException异常。
接着,我们需要在方法中增加用于处理文件内容的代码。这里我们使用JSON库来解析JSON文件。因此,需要在方法中添加以下代码:
```
JSONObject jsonObject = JSON.parseObject(sb.toString());
JSONArray subjectsList = jsonObject.getJSONArray("subjectsList");
```
这段代码用于解析JSON文件中的内容,并获取其中的"subjectsList"数组。
最后,我们需要计算GPA并返回GPA对象。可以在方法中添加以下代码:
```
Double weighteGpa = 0.0;
Double totalCredit = 0.0;
Double totalGrade = 0.0;
for (int i = 0; i < subjectsList.size(); i++) {
JSONObject subject = subjectsList.getJSONObject(i);
String subjectName = subject.getString("subject");
JSONObject creditJson = jsonObject2.getJSONObject(subjectName);
Double credit = creditJson.getDouble("credit");
Double grade = subject.getDouble("grade");
weighteGpa += credit * grade;
totalCredit += credit;
totalGrade += grade;
}
Double avgGrade = totalGrade / subjectsList.size();
Double gpa = (weighteGpa / (10 * totalCredit)) - 5;
return new GPA(String.format("%.1f", avgGrade), String.format("%.1f", gpa));
```
这段代码用于根据解析出来的数据计算GPA,并返回GPA对象。
最终的代码如下所示:
```
public static GPA PersonalReader(String file) throws IOException {
// Read credit information from a JSON file
try {
File f = new File(file);
if (!f.exists()) {
throw new FileNotFoundException("File not found: " + file);
}
FileReader fileReader = new FileReader(file);
Reader reader = new InputStreamReader(new FileInputStream(f), "Utf-8");
int ch = 0;
StringBuffer sb = new StringBuffer();
while ((ch = reader.read()) != -1) {
sb.append((char) ch);
}
reader.close();
fileReader.close();
File file1 = new File("C:\\Users\\isabe\\Desktop\\code\\code\\src\\credit.json");
FileReader fileReader1 = new FileReader(file1);
Reader reader1 = new InputStreamReader(new FileInputStream(file1), "Utf-8");
int ch1 = 0;
StringBuffer sb2 = new StringBuffer();
while ((ch1 = reader1.read()) != -1) {
sb2.append((char) ch1);
}
fileReader1.close();
reader1.close();
String creditStr = sb2.toString();
JSONObject jsonObject2 = JSON.parseObject(creditStr);
JSONObject jsonObject = JSON.parseObject(sb.toString());
JSONArray subjectsList = jsonObject.getJSONArray("subjectsList");
Double weighteGpa = 0.0;
Double totalCredit = 0.0;
Double totalGrade = 0.0;
for (int i = 0; i < subjectsList.size(); i++) {
JSONObject subject = subjectsList.getJSONObject(i);
String subjectName = subject.getString("subject");
JSONObject creditJson = jsonObject2.getJSONObject(subjectName);
Double credit = creditJson.getDouble("credit");
Double grade = subject.getDouble("grade");
weighteGpa += credit * grade;
totalCredit += credit;
totalGrade += grade;
}
Double avgGrade = totalGrade / subjectsList.size();
Double gpa = (weighteGpa / (10 * totalCredit)) - 5;
return new GPA(String.format("%.1f", avgGrade), String.format("%.1f", gpa));
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
```
public String kaoshilist4() { HttpServletRequest request = ServletActionContext.getRequest(); String truename = request.getParameter("truename"); String username = request.getParameter("username"); StringBuffer sb = new StringBuffer(); sb.append(" where "); StringBuffer sb2 = new StringBuffer(); sb2.append(" where "); if(username!=null&&!"".equals(username)){ sb.append(" user.username like '%"+username+"%'"); sb.append(" and "); sb2.append(" user.username like '%"+username+"%'"); sb2.append(" and "); request.setAttribute("username", username); } if(truename!=null&&!"".equals(truename)){ sb.append(" user.truename like '%"+truename+"%'"); sb.append(" and "); sb2.append(" user.truename like '%"+truename+"%'"); sb2.append(" and "); request.setAttribute("truename", truename); } sb.append(" 1=1 order by id desc"); String where = sb.toString(); sb2.append(" 1=1 "); String where2 = sb2.toString(); int currentpage = 1; int pagesize = 20; if (request.getParameter("pageNum") != null) { currentpage = Integer.parseInt(request.getParameter("pageNum")); pagesize = Integer.parseInt(request.getParameter("numPerPage")); } int total = kaoshiDao.selectBeanCount(where2); request.setAttribute("list", kaoshiDao.selectBeanList((currentpage - 1)* pagesize, pagesize, where)); request.setAttribute("totalCount", total); request.setAttribute("ps", pagesize); request.setAttribute("pn", currentpage); request.setAttribute("url", "method!kaoshilist4"); this.setUrl("kaoshi/kaoshilist4.jsp"); return SUCCESS; }解释此代码
此代码是一个 Java Web 应用的一个 Action,用于返回考试列表的数据。主要实现逻辑是通过从 request 中获取参数,并拼接成查询语句,在数据库中查找对应的数据。其中,pageNum 和 numPerPage 是用于分页查询的参数,totalCount 是查询结果的总数,ps 和 pn 是分页需要的参数,url 是分页查询的链接地址。最终将查询结果和相应的参数设置到 request 中,然后跳转到 kaoshi/kaoshilist4.jsp 页面进行展示。