我已经查看了有关从 main 方法访问对象实例的所有其他 stackoverflow 问题，但我尝试过的任何方法都不起作用，我仍然继续收到以下错误消息
java.59: error: cannot find symbol
System.out.println(student2.getStudentId());
这是我的主要方法:
import java.util.Scanner;
import java.io.*;
import java.util.Arrays;
public class Testing {
public static void main (String [] args) throws IOException {
final String INPUT_FILE = "c:\\Users\\XXXXXX\\Documents\\Input01.txt";
Scanner br = new Scanner(new File(INPUT_FILE));
// Test 2 - Test first and second line of information from input file
String[] strArray;
while (br.hasNext()) {
strArray = br.nextLine().split(",");
if(strArray[0].equals("STUDENT")) {
processStudentData(strArray);
System.out.println(student2.getStudentId());
}
else
if(strArray[0].equals("GRADE ITEM")) {
processGradeItemData(strArray);
}
}
} //end main
// ***************************************************************
// Uses string array from input file to create new student object
public static void processStudentData(String[] a) {
System.out.println("Running Test 2a:");
if (a[1].equals("ADD")) {
Student student2 = new Student(a[2], a[3], a[4], a[5]);
}
} // End processStudentData
} //end Testing
这是我的学生类(class)精简版:
public class Student {
private String studentId; // Unique ID for each Student
private String studentFirstName; // Student's legal first name
private String studentLastName; // Student's legal last name
private String studentEmail; // Student's school email address
//************************************************************************
Student() {
} // end Student
//************************************************************************
public Student(String studentId, String studentFirstName, String studentLastName,
String studentEmail) {
if (studentId.equals("")) {
throw new IllegalArgumentException("Student ID cannot be blank.");
}
if (studentFirstName.equals("")) {
throw new IllegalArgumentException("Student first name cannot be blank.");
}
if (studentLastName.equals("")) {
throw new IllegalArgumentException("Student last name cannot be blank.");
}
if (studentEmail.equals("")) {
throw new IllegalArgumentException("Student email cannot be blank.");
}
if (!studentEmail.contains("@")) {
throw new IllegalArgumentException("Student email must have '@'.");
}
this.studentId = studentId;
this.studentFirstName = studentFirstName;
this.studentLastName = studentLastName;
this.studentEmail = studentEmail;
} // end Student
//************************************************************************
public String getStudentId() {
return studentId;
} // end getStudentId
我需要能够使用主方法中的 get 方法打印出学生信息，但仍然通过 processStudentData 方法实例化 Student2 对象。我不想将 get 方法更改为静态，因为会有多个实例。
任何帮助将不胜感激。
更新:我已经添加了对 processStudentData 方法的返回，但仍然收到与以前相同的错误(主要方法没有更改，下面更新了 processStudentData 方法):
public static Student processStudentData(String[] a){
System.out.println("Running Test 2a:");
if (a[1].equals("ADD")) {
Student student2 = new Student(a[2], a[3], a[4], a[5]);
return student2;
}
return null;
}
最佳答案
由于 student2 被定义为 processStudentData 的 if 语句中的局部变量，因此它只能在该上下文中使用(其定义)
// Uses string array from input file to create new student object
public static void processStudentData(String[] a) {
System.out.println("Running Test 2a:");
if (a[1].equals("ADD")) {
Student student2 = new Student(a[2], a[3], a[4], a[5]);
}
} // End processStudentData
“一个”解决方案是将结果返回给调用者......
// Uses string array from input file to create new student object
public static Student processStudentData(String[] a) {
System.out.println("Running Test 2a:");
if (a[1].equals("ADD")) {
return new Student(a[2], a[3], a[4], a[5]);
}
return null;
} // End processStudentData
然后你可以使用它，比如......
Student student = processStudentData(strArray);
if (student != null) {
System.out.println(student.getStudentId());
}
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关于Java - 当从另一个方法创建对象时，尝试从主方法中打印对象的 get 方法，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/52472490/