Sorting collection of String and StringBuffer in Java

Last Updated : 09 Nov, 2020
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Sorting a collection of objects can be done in two ways: 

Read more about Comparable and Comparator
For sorted Collection we can use below collections: 

  • TreeSet
  • TreeMap

In case of String, sorting will be done automatically in natural order. 

Java 
// Java program to sort String objects using TreeSet
import java.util.Set;
import java.util.TreeSet;

public class Test {
    public static void main(String[] args)
    {
        Set<String> str = new TreeSet<String>();
        str.add("Sohan");
        str.add("Raja");
        str.add("Harish");
        str.add("Ram");
        System.out.println(str);
    }
}

Output:  

[Harish, Raja, Ram, Sohan]
Java 
// Java program to demonstrate that simple sorting
// StringBuffer objects does work.
import java.util.Set;
import java.util.TreeSet;

public class Test {

    public static void main(String[] args)
    {
        Set<StringBuffer> str = new TreeSet<>();
        str.add(new StringBuffer("Sohan"));
        str.add(new StringBuffer("Raja"));
        str.add(new StringBuffer("Harish"));
        str.add(new StringBuffer("Ram"));
        System.out.println(str);
    }
}

Output
[Harish, Raja, Ram, Sohan]

String class implements Comparable interface whereas StringBuffer and StringBuilder classes do not implement Comparable interface. See below signatures of String, StringBuffer and StringBuilder classes: 

Java 
public final class String
    extends Object
        implements Serializable,
    Comparable, CharSequence
Java 
public final class StringBuffer
    extends Object
        implements Serializable,
    CharSequence
Java 
public final class StringBuilder
    extends Object
        implements Serializable,
    CharSequence

There are many ways of sorting StringBuffer, StringBuilder classes. Some of the ways are given below: 

  • By implementing Comparator interface
  • By converting StringBuffer to String using StringBuffer.toString() method
Java 
// Java program to demonstrate sorting
// of StringBuffer objects using Comparator
// interface.
import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;

public class Test implements Comparator<StringBuffer> {
    @Override public int compare(StringBuffer s1, StringBuffer s2)
    {
        return s1.toString().compareTo(s2.toString());
    }

    public static void main(String[] args)
    {
        Set<StringBuffer> str = new TreeSet<>(new Test());
        str.add(new StringBuffer("Sohan"));
        str.add(new StringBuffer("Raja"));
        str.add(new StringBuffer("Harish"));
        str.add(new StringBuffer("Ram"));
        System.out.println(str);
    }
}

Output: 

[Harish, Raja, Ram, Sohan]


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equals() on String and StringBuffer objects in Java

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Sajid Ali Khan
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