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    <p>You can make your object comparable:</p> <pre><code>public static class MyObject implements Comparable&lt;MyObject&gt; { private Date dateTime; public Date getDateTime() { return dateTime; } public void setDateTime(Date datetime) { this.dateTime = datetime; } @Override public int compareTo(MyObject o) { return getDateTime().compareTo(o.getDateTime()); } } </code></pre> <p>And then you sort it by calling:</p> <pre><code>Collections.sort(myList); </code></pre> <p>However sometimes you don't want to change your model, like when you want to sort on several different properties. In that case, you can create comparator on the fly:</p> <pre><code>Collections.sort(myList, new Comparator&lt;MyObject&gt;() { public int compare(MyObject o1, MyObject o2) { return o1.getDateTime().compareTo(o2.getDateTime()); } }); </code></pre> <p>However, the above works only if you're certain that dateTime is not null at the time of comparison. It's wise to handle null as well to avoid NullPointerExceptions:</p> <pre><code>public static class MyObject implements Comparable&lt;MyObject&gt; { private Date dateTime; public Date getDateTime() { return dateTime; } public void setDateTime(Date datetime) { this.dateTime = datetime; } @Override public int compareTo(MyObject o) { if (getDateTime() == null || o.getDateTime() == null) return 0; return getDateTime().compareTo(o.getDateTime()); } } </code></pre> <p>Or in the second example:</p> <pre><code>Collections.sort(myList, new Comparator&lt;MyObject&gt;() { public int compare(MyObject o1, MyObject o2) { if (o1.getDateTime() == null || o2.getDateTime() == null) return 0; return o1.getDateTime().compareTo(o2.getDateTime()); } }); </code></pre>
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    1. COGood answer. Why do you need to include the versions without null checking? What is the advantage? If the correct way is the second you can only include it and make the important info more attractive.
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    2. COTwo reasons - simplicity and fail-fast. You want code to be as simple as possible, and if you are certain that your property should not be null you probably want your code to fail as soon as possible if you encounter null, instead passing invalid data on and breaking even further from the place where invalid data was introduced.
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    3. COif o1 or o2 is null, return 0; //this line might cause bug as returning 0 implies that they're equal.
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