用于在java中创建对象数组的空指针异常

Question

我已经检查了几乎所有类型的对象数组的声明.请建议所需的更改.此代码给我一个空指针异常,如下所示:

objarray.main(objarray.java:33)中线程"main"java.lang.NullPointerException中的异常

import java.util.*;
class Prod {
    private int    pno, pcost;
    private String pname;

    void accept() {
        Scanner sc = new Scanner( System.in );
        System.out.println( "Enter pno" );
        pno = sc.nextInt();
        System.out.println( "Enter pname" );
        pname = sc.next();
        System.out.println( "Enter pcost" );
        pcost = sc.nextInt();
    }

    void print() {
        System.out.println( pno + "\t" + pname + "\t" + pcost );
    }
}

class objarray {
    public static void main( String[] args ) {
        int i;
        Prod[] p = new Prod[3];
        for( i = 0; i < 3; i++ )
            p[i].accept();
        for( i = 0; i < 3; i++ )
            p[i].print();
    }
}

Answer 1

您需要初始化数组的元素:

Prod[] p = new Prod[3];
for(i = 0;i<3;i++)
    p[i] = new Prod(); // added this line
    // rest of code

该语句Prod[] p = new Prod[3];只为对象的引用分配空间 - 它不会创建它们.Prod