打印數組-覆蓋toString（）方法

Question

我有兩個不同的班級，Student和StudentTest-學生班級有；

public class Student {

// Data Members 
private String name; // The name of this student
private long idNumber; // The ID number of this student

// Constructs a new Student with passed name and ID number parameters.
public Student(String studentName, long studentIDNumber) {
name = studentName;
idNumber = studentIDNumber;
}

// Returns the name of this student.
public String getName() {
return name;
}

// Returns the ID number of this student.
public long getIDNumber() {
return idNumber;
}

// Sets the name of this student.
public void setName(String studentName) {
name = studentName;
}

// Sets the ID number of this student.
public void setIDNumber(long studentIDNumber) {
idNumber = studentIDNumber;
}

@Override
public String toString(){
    return "Name: " + this.name;
}

} // end class

StudentTest類具有3種不同的方法：1.要求用戶輸入數組的大小，然后創建類型為Student的數組； 2.要求用戶用名稱和ID號填充數組； 3.要求顯示數組的內容。

import java.util.Scanner; 

public class StudentTest { 

// Main method.
public static void main(String [] args) {

    Student[] students = createArray();
    populateArray(students);
    displayArray(students);
}

// Method that asks user for size of array.
public static Student[] createArray() {

System.out.println("Enter size of array: ");
Scanner userInputEntry = new Scanner(System.in);
int inputLength = userInputEntry.nextInt();
Student students[] = new Student[inputLength];

return students; 

}

// Method that asks user to populate array.
public static void populateArray(Student [] array) {

    for(int i = 0; i < array.length; i++) {
        array[i] = new Student();
        System.out.println("Enter student name: ");
        Scanner userInputEntry = new Scanner(System.in);
        array[i].setName(userInputEntry.next());
        System.out.println("Enter student ID number: ");
        array[i].setIDNumber(userInputEntry.nextLong());
    }

}

// Method that displays contents of array.
public static void displayArray(Student[] array) {

    for(int i = 0; i < array.length; i++){
        System.out.println(array[i].toString());
    }

}

}

當我嘗試運行它時，出現關於

 array[i] = new Student();

在第二種方法的for循環中。

Answer 1

您希望它如何工作？

@Override
public void toString(){
    return "Name: " + this.name;
}

它應該給您一個編譯錯誤。 您正在嘗試發送回一個字符串，並且返回類型為空。

更改為

@Override
public String toString(){
    return "Name: " + this.name;
}

將您的主要方法更改為

// Main method.
public static void main(String [] args) {
    Student[] students = createArray();
    populateArray(students);
    displayArray(students)
}