Question

这是在不使用java哈希函数的情况下实现散列的代码。我收到了错误java.lang.NullPointerException

用于创建与电话和姓名联系的班级：

public class Contact {
  String name;
  int phone;
}

public class Hash {
  public static void main(String[] args) {

    Contact[] table = new Contact[1009];

    int tableSize = 1009;

    int out = calcHash("Ahmed", tableSize);

    table[out].name = "Ahmed";    //This line has an error
    table[out].phone = 23445677;  //This line has an error

    System.out.println(out);

  }

为名称生成哈希值的方法：

  public static int calcHash(String key, int tableSize) {


    int i, l = key.length();
    int hash = 0;
    for (i = 0; i < l; i++) {

      hash += Character.getNumericValue(key.charAt(i));
      hash += hash << 10;
      hash ^= hash >> 6;
    }
    hash += hash << 3;
    hash ^= hash >> 11;
    hash += hash << 15;
    if (hash > 0) return hash % tableSize;
    else return -hash % tableSize;
  }
}

Hash类中的这些行抛出异常：

table[out].name = "Ahmed";    //This line has an error
table[out].phone = 23445677;  //This line has an error

Answer 1

执行以下行时，

table[Out]为空：

table[Out].Name = "Ahmed";

在设置属性之前，尝试将table[Out]设置为新实例：

table[Out] = new contact();
table[Out].Name = "Ahmed";    
table[Out].phone = 23445677;

声明对象并为数组分配索引后，我收到空错误

1 个答案: