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  1. #1
    jumpman8947 is offline Member
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    Default ArrayList indexOf

    Hi i'm just studying over ArrayLists and i have encountered a problem, i'm trying to get the index of an element but it keeps returning -1. Here's the code
    Java Code:
    import java.util.ArrayList;
    
    
    public class PhoneEntry {
    	String name;
    	String phone;
    	
    public PhoneEntry(String name, String phone) {
    	this.name = name;
    	this.phone = phone;
    	}
    	public static void main(String[] args){
    
    	ArrayList<PhoneEntry> theDirectory = new ArrayList<PhoneEntry>();
    	theDirectory.add(new PhoneEntry("Jane","12"));
    	System.out.println(theDirectory.size());
    	int index = theDirectory.indexOf(new PhoneEntry("Jane","12"));
    	System.out.println(index);
    	}
    
    	
    }
    I know the list is not empty because it returns a size.

  2. #2
    jim829 is offline Senior Member
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    Default Re: ArrayList indexOf

    This will never work because the default implementation only checks for reference equality. Your class PhoneEntry must implement the equals() method. And you should usually implement the hashCode() method too. Here is an example --> Object as a Superclass (The Java Tutorials > Learning the Java Language > Interfaces and Inheritance)

    Regards,
    Jim
    The JavaTM Tutorials | SSCCE | Java Naming Conventions
    Poor planning on your part does not constitute an emergency on my part

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