java - 在 java 中传递数组时代码中的意外输出

Question

我一直面临在 java 中传递数组的问题。代码是:

package input_output;

import static java.lang.System.out;
import java.util.Scanner;

public class InputOutput {
    private static Scanner sc;
    public static void main(String []args){
        sc = new Scanner(System.in);
        out.print("Enter the length of arrays   :\t");
        int n = sc.nextInt();
        Employee[] emp = new Employee[n];
        for(int i=0;i<n;i++){
            out.print("\nEnter name and age of " + (i+1) + " employee   :\t");
            emp[i] = new Employee();
            emp[i].setName(sc.nextLine());
            sc.nextLine();
            emp[i].setAge(sc.nextInt());
        }

        Operation operate = new Operation(emp,n);

        operate.printOnScreen();

    }
}

class Operation{ 
    Employee []emp;
    public Operation(Employee[] emp,int n){
        this.emp=emp;
        for(Employee e: this.emp)
          e = new Employee();
    }

    public void printOnScreen() { 
        for(Employee e : emp){
            e = new Employee();
            out.println("Name:\t" + e.getName() + "\t\tAge:\t" + e.getAge() + "\n");
        }
    }
}

Employee 类是一个简单的 bean，包含年龄和姓名的 getter 和 setter 方法。

输出来了:

Name: null
Age:0

我的错误是什么？

---

现在我已经将构造函数更改为

public Operation(Employee[] emp, int n){
        this.emp=emp;
}

并删除了行:

e = new Employee(); 

来自 PrintOnScreen()

输出是:

Name:
Age:21

Answer 1

您没有在以下代码中从数组输出数据:

public void printOnScreen() 
{ 
    for(Employee e : emp)
    {
        e = new Employee(); // <<< THIS IS WRONG, AS e IS ALREADY SET BY LOOP!!
        out.println("Name:\t" + e.getName() + "\t\tAge:\t" + e.getAge() + "\n");
    }
}

此代码在循环的每次迭代中创建一个新的 e => 您不是从数组中输出条目，而是新创建的条目。代码应该是这样的

public void printOnScreen() 
{ 
    for(Employee e : emp)
    {
        out.println("Name:\t" + e.getName() + "\t\tAge:\t" + e.getAge() + "\n");
    }
}

---

此外，以下代码没有意义:

public Operation(Employee[] emp,int n){
    this.emp=emp;
    for(Employee e: this.emp)
      e = new Employee();
}

为什么要遍历 this.emp 中的所有员工以创建无处存储的新 Employee 实例？此外，不使用 n 参数。此代码应为:

public Operation(Employee[] emp)
{
    this.emp=emp;
}