从方法返回数组（似乎不起作用）

Question

import java.util.*;

public class test2 {

public static void main(String[] args){
int[] list = {1,2,3,4,5,6,7};
int[] list2 = reverse(list);
 System.out.print(list2);
}

public static int[] reverse(int[] list){
    int[] result = new int[list.length];

    for(int i=0, j=list.length-1; i<list.length; i++,j--){
        result[j] = list[i];}

    return result;  }

}

it is a code from my textbook. But when I print list2, it shows this weird message : [I@7b963273 I have no idea what is wrong with the code. Plz help me!

Answer 1

The array of primitive types is an object itself . When you print it using System.out.print() , it calls toString() method of Object class. Which is defined like this in Object class:

public String  toString() {
        return getClass().getName() + "@" + Integer.toHexString(hashCode());
    }

to print the returned array you use:

System.out.println(Arrays.toString(list2));

EDIT
If you want to return an array from method you should do exactly how you did in your code.

suppose that 'merge' is a method and arr1 and arr2 are arrays then you can do like this:

public static int[] merge(int arr1[], int arr2[])
{
  int[] result = new int[arr1.length + arr2.length];
  int counter = 0 ;
  for ( int i =0 ;i < result.length ; i++)
  {
    if ( i >= arr1.length)
    {
      result[i] = arr2[counter++];
    }
    else
    {
      result[i] = arr1[i];
    }
  }
 return result;
}

And then you can print the merge as:

System.out.println(Arrays.toString(merge(arr1,arr2));

Answer 2

You're calling toString() (implicitly) directly on an array. Arrays don't override toString() , so you get the default implementation from Object :

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode()) 

So in your output, the [I part is the "name" of the int[] class (print int[].class.getName() and it will show the same thing) and the number is the hash code of the array in hex. (Which again isn't overridden - it doesn't take account of the contents of tha array.)

This has nothing to do with where the array has come from - you'd get the same kind of output (with a different number) if you called:

System.out.print(list);

before the reverse call.

You should use Arrays.toString(int\\[\\]) :

System.out.println(Arrays.toString(list2));

Answer 3

System.out.println(list2); invokes Object#toString() method which returns the combination of Classname+@+Hex_Number_Of_Hashcode .

you have to use overloaded Arrays.toString(list2) ; to print the string representation of your array.