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POHow to sort a collection using Collection.sort()
 

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    <p>I am writing a program that stores an <code>ArrayList</code> of <code>Person</code> objects (input is from a text file).</p> <p>This is the code for the <code>Person</code> class, which I will create <code>Person</code> objects from:</p> <pre><code>import java.io.Serializable; public class Person implements Comparable&lt;Person&gt;, Serializable { private String firstName; private String lastName; private int age; public Person(String firstName, String lastName, int age) { this.firstName = firstName; this.lastName = lastName.toUpperCase(); this.age = age; } public int getAge() { return age; } public String getName() { return firstName; } /** * @return a String of the details of a person in the format: * Name: &lt;firstName&gt; &lt;lastName&gt; Age: &lt;age&gt; */ public String toString() { return "Name: " + firstName + "" + lastName + "\t\t" + "Age: " + age; } /** * Compare the age of the current instance of Person to another age of the specified Person * @return negative number this &lt; p * @return 0 if this == p * @return positive number if this &gt; p */ public int compareTo(Person p) { return ((Integer)this.getAge()).compareTo(p.getAge()); } </code></pre> <p>And I created a <code>Comparable</code> interface:</p> <pre><code>public interface Comparable&lt;T&gt; { public int compareTo(T o); } </code></pre> <p>And here is the code for the class called <code>Collection</code> which will create an <code>ArrayList</code> to store <code>Person</code> objects, I ommitted parts of the code that were not relevant as it is long:</p> <pre><code>import java.io.*; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; import java.util.StringTokenizer; import java.util.Iterator; public class Collection { private ArrayList&lt;Person&gt; people; public Collection() { people = new ArrayList&lt;Person&gt;(); } public void readFromFile(String filename) { // code that will get input to assign values to fields to a Person Person newPerson = new Person(firstNameToken, lastNameToken, ageToken); } /** * Prints the details of each person held in the people ArrayList */ public void printDetails() { Iterator&lt;Person&gt; it = people.iterator(); while(it.hasNext()) { Person p = it.next(); System.out.println(p.toString()); } } public static void main(String [] args) throws FileNotFoundException { Collection c = new Collection(); // check //for(Person person : c.people) //{ // System.out.println(person); //} Collections.sort(c.people); } } </code></pre> <p>However I get this error, the sort does not work:</p> <blockquote> <p>Exception in thread "main" java.lang.Error: Unresolved compilation problem: Bound mismatch: The generic method sort(List) of type Collections is not applicable for the arguments (ArrayList). The inferred type Person is not a valid substitute for the bounded parameter ></p> </blockquote> <p>Does anyone know why? I am looking furiously around on google for solutions, I can't see what I am missing. I've implemented comparable..</p>
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