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POHow to use Comparator in Java to sort
 

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    <p>I learned how to use the comparable but I'm having difficulty with the Comparator. I am having a error in my code: </p> <pre><code>Exception in thread "main" java.lang.ClassCastException: New.People cannot be cast to java.lang.Comparable at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.sort(Unknown Source) at java.util.Collections.sort(Unknown Source) at New.TestPeople.main(TestPeople.java:18) </code></pre> <p>Here is my code:</p> <pre><code>import java.util.Comparator; public class People implements Comparator { private int id; private String info; private double price; public People(int newid, String newinfo, double newprice) { setid(newid); setinfo(newinfo); setprice(newprice); } public int getid() { return id; } public void setid(int id) { this.id = id; } public String getinfo() { return info; } public void setinfo(String info) { this.info = info; } public double getprice() { return price; } public void setprice(double price) { this.price = price; } public int compare(Object obj1, Object obj2) { Integer p1 = ((People) obj1).getid(); Integer p2 = ((People) obj2).getid(); if (p1 &gt; p2) { return 1; } else if (p1 &lt; p2){ return -1; } else { return 0; } } } </code></pre> <pre class="lang-java prettyprint-override"><code>import java.util.ArrayList; import java.util.Collections; public class TestPeople { public static void main(String[] args) { ArrayList peps = new ArrayList(); peps.add(new People(123, "M", 14.25)); peps.add(new People(234, "M", 6.21)); peps.add(new People(362, "F", 9.23)); peps.add(new People(111, "M", 65.99)); peps.add(new People(535, "F", 9.23)); Collections.sort(peps); for (int i = 0; i &lt; peps.size(); i++){ System.out.println(peps.get(i)); } } } </code></pre> <p>I believe it has to do something with the casting in the compare method but I was playing around with it and still could not find the solution</p>
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    1. CODon't use raw types in new code http://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it ; use `Comparator<People>`, `Comparable<People>`, `List<People>`, etc.
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    2. COI changed the Comparator<People> but when I change Arraylist<People>, the Collections.sort gets an error
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    3. COread my answer about the 2 overloads of `sort`. If you're told to use `Comparator<People>`, then use the 2-argument `sort`, not the 1-argument `sort` (which requires `People implements Comparable<People>`).
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