Sorting an array using Comparator

Question

I have the following code. When I try to compile it, it gives me the following error:

The method sort(List<T>, Comparator<? super T>) in the type Collections is not 
applicable for the arguments (Software[], new Comparator(){}) 
The type new Comparator(){} must implement the inherited abstract method
Comparator.compare(Object, Object)

Code

import java.text.DecimalFormat; // For proper currency  
import java.util.Comparator;
import java.util.Collections;


public class Software

{
// Declare variables

String SoftwareTitle; // SoftwareTitle
int SoftwareStock;    // Software totals
double SoftwarePrice; // Software Price
int SoftwareNum;      // Software Product ID
double CalculateInventory;  // To add inventory
double SoftwareValue;       // Software Total value
double value;               // Complete inventory total

Software( String softtitle, int softstock, double softprice, int softitemnum )

{
    // Create object constructor

    SoftwareTitle = softtitle;
    SoftwareStock = softstock;
    SoftwarePrice = softprice;
    SoftwareNum = softitemnum;

    } 

    // Set Software Title

    public void setSoftwareTitle( String softtitle )
    {
        SoftwareTitle = softtitle;
    } 


    // Return Software Title

    public String getSoftwareTitle()
    {
        return SoftwareTitle;
    } 

    // Set software inventory
    public void setSoftwareStock( int softstock)
    {
        SoftwareStock = softstock;
    } 

    // Return software inventory
    public int getSoftwareStock()
    {
        return SoftwareStock;
    }

    // Set software price

    public void setSoftwarePrice( double softprice )
    {
        SoftwarePrice = softprice;
    }

    // Return software price
    public double getSoftwarePrice()
    {
        return SoftwarePrice;

    }

    // Set item number

    public void setSoftwareNum( int softitemnum )
    {
        SoftwareNum = softitemnum;
          }         //

    //return software item number

    public int getSoftwareNum()
    {
        return SoftwareNum;
    } //


    // calculate inventory value

    public double Softwarevalue()
    {
        return SoftwarePrice * SoftwareStock;

    } 

    public void setCalculateInventory (double value){
        this.CalculateInventory = value;
    }



    public double getCalculateInventory(){
        double value = 0;
        for(int i = 0; i < 3; i++){
            value = Softwarevalue();
        }
        return value;
    }


 }//end method value

 //

import java.text.DecimalFormat; // For proper currency  
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;


 public class Inventory {

public static void main( String args[] )

{

    // Start array of software titles

    Software[] aSoftware = new Software[4];

    aSoftware[0]= new Software("Command and Conquer ", 6, 29.99, 10122); 
        aSoftware[1]= new Software("Alice in Wonderland", 1, 10.99,10233);
        aSoftware[2]= new Software("Doom", 1, 10.99, 10344);
    aSoftware[3]= new Software("Walking Dead", 6, 9.99, 10455);

//Set currency format
    DecimalFormat money = new DecimalFormat("$0.00");

// Sort in order of Software Name

    Collections.sort(aSoftware, new Comparator() {
    public int compare(Software s1, Software s2) {
    return s1.getSoftwareTitle().compareTo(s2.getSoftwareTitle());

                }
            });



// Display software title, number of units, cost, item number and total inventory

     for (int i = 0; i < aSoftware.length; i++){    

System.out.println("Software Title is "+ aSoftware[i].getSoftwareTitle() );

System.out.println("The number of units in stock is "+    aSoftware[i].getSoftwareStock() );

System.out.println("The price of the Software Title is "+ (money.format(aSoftware[i].getSoftwarePrice() )));

System.out.println( "The item number is "+ aSoftware[i].getSoftwareNum());

System.out.println( "The value of the Software Inventory is "+  (money.format(aSoftware[i].Softwarevalue() )));

System.out.println();   
            }

//output total inventory value

double total = 0.0;
    for (int i = 0; i < 3; i++){ 
    total +=  aSoftware[i].getCalculateInventory();            
        }
    System.out.printf("Total Value of Software Inventory is: \t$%.2f\n", total);


//end output total inventory value








 }
 }

 //

 //end 

How do I get the software titles (an array) to display in alphabetical order using the Comparator?

Answer 1

You've got two problems:

1) You're using Collections.sort (which takes a List<E> ), but trying to sort an array. Use Arrays.sort instead.

2) You need to specify that you're implementing Comparator<Software> , not just the raw Comparator type.

So basically, this works:

Arrays.sort(aSoftware, new Comparator<Software>() {
    public int compare(Software s1, Software s2) {
        return s1.getSoftwareTitle().compareTo(s2.getSoftwareTitle());
    }
});

Answer 2

Firstly: to sort an array, such as Software[] , you need to use java.util.Arrays.sort rather than java.util.Collections.sort .

Secondly: since your Comparator is specifically for Software instances, you should write new Comparator<Software>() rather than merely new Comparator() . (The latter is actually bad code even when it does work.)

Answer 3

You can't sort on array when using Collections.sort . Collections.sort accepts only List. user Arrays.sort rather than Collection.sort .

Answer 4

Because you are trying to use array of object use below:

Arrays.sort(aSoftware);

and your software class should implements implements Comparable and override its compareTo method:

@Override
public int compareTo(Software o) {
    return this.getSoftwareTitle().compareTo(o.getSoftwareTitle());
}

I have made correction to your class as below:

public class Software implements Comparable<Software>{
// Declare variables

String SoftwareTitle; // SoftwareTitle
int SoftwareStock; // Software totals
double SoftwarePrice; // Software Price
int SoftwareNum; // Software Product ID
double CalculateInventory; // To add inventory
double SoftwareValue; // Software Total value
double value; // Complete inventory total

Software(){

}

Software(String softtitle, int softstock, double softprice, int softitemnum)

{
    // Create object constructor

    SoftwareTitle = softtitle;
    SoftwareStock = softstock;
    SoftwarePrice = softprice;
    SoftwareNum = softitemnum;

}

// Set Software Title

public void setSoftwareTitle(String softtitle) {
    SoftwareTitle = softtitle;
}

// Return Software Title

public String getSoftwareTitle() {
    return SoftwareTitle;
}

// Set software inventory
public void setSoftwareStock(int softstock) {
    SoftwareStock = softstock;
}

// Return software inventory
public int getSoftwareStock() {
    return SoftwareStock;
}

// Set software price

public void setSoftwarePrice(double softprice) {
    SoftwarePrice = softprice;
}

// Return software price
public double getSoftwarePrice() {
    return SoftwarePrice;

}

// Set item number

public void setSoftwareNum(int softitemnum) {
    SoftwareNum = softitemnum;
} //

// return software item number

public int getSoftwareNum() {
    return SoftwareNum;
} //

// calculate inventory value

public double Softwarevalue() {
    return SoftwarePrice * SoftwareStock;

}

public void setCalculateInventory(double value) {
    this.CalculateInventory = value;
}

public double getCalculateInventory() {
    double value = 0;
    for (int i = 0; i < 3; i++) {
        value = Softwarevalue();
    }
    return value;
}

@Override
public int compareTo(Software o) {
    return this.getSoftwareTitle().compareTo(o.getSoftwareTitle());
}





}// end method value

Your Inventory class:

public class Inventory {

public static void main(String args[])

{

    // Start array of software titles

    Software[] aSoftware = new Software[4];

    aSoftware[0] = new Software("Command and Conquer ", 6, 29.99, 10122);
    aSoftware[1] = new Software("Alice in Wonderland", 1, 10.99, 10233);
    aSoftware[2] = new Software("Doom", 1, 10.99, 10344);
    aSoftware[3] = new Software("Walking Dead", 6, 9.99, 10455);

    // Set currency format
    DecimalFormat money = new DecimalFormat("$0.00");

    Arrays.sort(aSoftware);



    // Display software title, number of units, cost, item number and total
    // inventory

    for (int i = 0; i < aSoftware.length; i++) {

        System.out.println("Software Title is "
                + aSoftware[i].getSoftwareTitle());

        System.out.println("The number of units in stock is "
                + aSoftware[i].getSoftwareStock());

        System.out.println("The price of the Software Title is "
                + (money.format(aSoftware[i].getSoftwarePrice())));

        System.out.println("The item number is "
                + aSoftware[i].getSoftwareNum());

        System.out.println("The value of the Software Inventory is "
                + (money.format(aSoftware[i].Softwarevalue())));

        System.out.println();
    }

    // output total inventory value

    double total = 0.0;
    for (int i = 0; i < 3; i++) {
        total += aSoftware[i].getCalculateInventory();
    }
    System.out.printf("Total Value of Software Inventory is: \t$%.2f\n",
            total);

    // end output total inventory value

}
}

Below is final output in sorted order:

Software Title is Alice in Wonderland
The number of units in stock is 1
The price of the Software Title is $10.99
The item number is 10233
The value of the Software Inventory is $10.99

Software Title is Command and Conquer 
The number of units in stock is 6
The price of the Software Title is $29.99
The item number is 10122
The value of the Software Inventory is $179.94

Software Title is Doom
The number of units in stock is 1
The price of the Software Title is $10.99
The item number is 10344
The value of the Software Inventory is $10.99

Software Title is Walking Dead
The number of units in stock is 6
The price of the Software Title is $9.99
The item number is 10455
The value of the Software Inventory is $59.94

Total Value of Software Inventory is:   $201.92

Answer 5

You should make your "Software" class implement comparable and then overwrite the compare method to return a compare on the titles like you did outside your code. This will be a replacement for the comparator. Then all you need to to is call Arrays.sort.