minimum value in java won't work

问题

I need help because my brain cells cannot find what is wrong with this program! Here's the code

     import java.util.*;
      public class student{
      public static void main (String []args)

    { 
        Scanner sc=new Scanner(System.in);
        System.out.println("enter number elements");  //asking the user to enter the number of integer items 
        int num=sc.nextInt();
        int []myArray= new int[num];
        int maxValue=myArray[0];
        int minValue=myArray[0];
        int i;
        for( i=0; i<myArray.length;i++)
        {System.out.print("Enter element"+(i+1));  //asking the user to enter the items 
           myArray[i]=sc.nextInt();
        }

        for(i=0; i<myArray.length;i++)
        {System.out.print(myArray[i]);    //displaying the elements 
        }
        System.out.println(" ");
        for( i=myArray.length-1; i>=0;i--)
        {System.out.print(myArray[i]);      //displaying the elements in a backward order
        }
        System.out.println(" ");
        for( i=0; i<myArray.length;i++)
        {if(i%2==1)

           System.out.println(myArray[i]);               //displaying the elements in odd indices

        }

      for( i=0; i<myArray.length-1;i++)
        { if(myArray[i]>maxValue)
            {
                maxValue= myArray[i];           //finding the maximum


            }

        }
        System.out.println(maxValue+" "+(i+1));

        for( i=1; i<myArray.length-1;i++)
        { if( myArray[i]<minValue)
            {minValue= myArray[i];                //finding the minimum

            }
        }
       System.out.println(+minValue+" "+(i+1));



        System.out.println(myArray[0]);                          //displaying first item
        System.out.println( myArray[myArray.length-1]);          //displaying last item




        for( i=0; i<myArray.length;i++)
        {if(i%2==0)

          {  myArray[i]= myArray[i]*-1;                    //multiplying items in even indices by -1

        System.out.print( myArray[i]);}
    }
  }

}

The program does what's in the comment, yet the minimum value is always zero even if I don't enter it...I cannot figure out what's the problem, so I'd appreciate your help!

回答1:

You initialize you array. And then default values are given (every int is initialized 0)

   int []myArray= new int[num];
   int minValue=myArray[0];

it will be 0

so nothing smaller can be found than zero if you type in positive integers

Solution First fill your array with the user input THEN do

 int minValue=myArray[0];

Or use Integer.MIN_VALUE.

回答2:

When you go through to look for either the minimum or maximum of a set of values, it's better to assume that all values will be larger than a default maximum value (i.e. set your maximum value to the smallest possible integer), and that all values will be smaller than a default minimum value (i.e. set your minimum value to be the largest possible integer).

The above sounds counterintuitive, but as you iterate through the array, if you come across a value that is "larger" than the maximum, you update your max value. The same idea applies for the minimum (i.e. if you find a value smaller than your minimum). Since both would start out at their logical extremes, you'll be able to find the true minimum/maximum easier.

The code

int maxValue=myArray[0];
int minValue=myArray[0];

implies that both maxValue and minValue are 0, since a primitive integer array will always populate itself with zeroes. Instead, you should try this:

int maxValue=Integer.MIN_VALUE;
int minValue=Integer.MAX_VALUE;

For some clarification on those Integer constants, check out Integer.MAX_VALUE and Integer.MIN_VALUE in the API.

回答3:

int minValue=myArray[0]; 

because of this line, your minValue is set to 0. So the minimum value would be reset in this method only if the myArray[i] in the below code is less than 0. Otherwise it remains 0.

 for( i=1; i<myArray.length-1;i++) 
        { 
           if( myArray[i]<minValue) 
            {
              minValue= myArray[i];                

            } 
        } 

回答4:

int []myArray= new int[num];

int array default elements to 0

来源：https://stackoverflow.com/questions/10839840/minimum-value-in-java-wont-work