Compare code in Java

What if you have a specific scenario where you want to first sort by rank and then alphabetically if the ranks are same?

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Any number of Comparator classes can be created to sort them differently as shown below. import java.util.Comparator;   public class JavaTechnologyComparator implements Comparator<JavaTechnology> {   @Override public int compare(JavaTechnology t1, JavaTechnology t2) {   //handle null values here Integer rank1 = t1.getRank(); Integer rank2 = t2.getRank(); int rankVal = rank1.compareTo(rank2); int nameVal = t1.getName().toLowerCase().compareTo(t2.getName().toLowerCase());   … Read more

Can you write a simple program that compares two objects to return if they are equal or not? This method will be handy in defining your own equals( ) method.

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This is usefull in domain or value object class to compare different object fields in an equals method public class DomainObject {   //protected because only inheriting domain classes can use it protected boolean isPropertyEqual(Object compare1, Object compare2) { // go here if compare1 is null, i.e. test cases 1 & 3 if (compare1 == … Read more

Now, what if you have your own custom class like a Dog, Cat, etc instead of a library class like String, Integer, etc?

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Here is an example of a JavaTechnology custom object that implements a default sorting logic based on the rank (i.e popularity). public class JavaTechnology implements Comparable<JavaTechnology>{   private String name; private int rank;   // popularity lower value means more popular   public JavaTechnology(String name, int rank){ this.name = name; this.rank = rank; }   //default … Read more

Is there anything wrong with the above code?

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Yes, 2 things — firstly, the above sort is case sensitive, that is the uppercase takes priority over lowercase pushing ‘Java’ after ‘JSP’. Secondly, if the collection had any null values, it will throw a NullpointerException. These two issues can be rectified by providing a custom sorting implementation that ignores case and handles null values … Read more

Can you write code to sort the following string values naturally (i.e. in alphabetical order)? (JEE, Java, Servlets, JMS, JNDI, JDBC, JSP, and EJB)

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Here is the sample code that makes use of the default compareTo( ) provided in the String class as it implements the Comparable interface and the Collections utility class that provides a sorting method, which internally uses the efficient “merge sort” algorithm. import java.util.Arrays; import java.util.Collections; import java.util.List;   public class Sort1 { public static … Read more