How to sort ArrayList in Java
Java Collections Tutorial List :
1:Introduction to Java Collections Framework 2:ArrayList in java with example programs 3:ArrayList Important methods 4:How to sort ArrayList in Java 5:Comparator and Comparable Interface in Java
To sort an ArrayList object, use Collection.sort method. This is a static method and it sorts an ArrayList object's elements into ascending order.
We have given two example of sorting an String ArrayList and Integer ArrayList.
Example 1: Sorting of ArrayList<string> :
In this example we are sorting the ArrayList of String type.simply call Collections.sort(arraylist) method. The output List will be sorted alphabetically.
package com.example;
import java.util.ArrayList;
import java.util.Collections;
public class ListSorting {
public static void main(String args[]) {
ArrayList<String> list = new ArrayList<String>();
list.add("Ravi");
list.add("Amit");
list.add("Neil");
list.add("Aayush");
System.out.println("Before Sorting list element is :");
for (String str : list) {
System.out.println(str);
}
Collections.sort(list);
/* List after sorting */
System.out.println("After Sorting list is:");
for (String str : list) {
System.out.println(str);
}
}
}
Output :
Before Sorting list element is : Ravi Amit Neil Aayush After Sorting list is: Aayush Amit Neil Ravi
Example 2: Sorting of ArrayList <integer> :
We can use same Collection.sort method to sort Integer ArrayList.
package com.example;
import java.util.ArrayList;
import java.util.Collections;
public class ListSorting {
public static void main(String args[]) {
ArrayList<Integer> list = new ArrayList<Integer>();
list.add(23);
list.add(35);
list.add(10);
list.add(45);
System.out.println("Before Sorting list element is :");
for (int value : list) {
System.out.println(value);
}
Collections.sort(list);
/* List after sorting */
System.out.println("After Sorting list is:");
for (int value : list) {
System.out.println(value);
}
}
}
Output :
Before Sorting list element is : 23 35 10 45 After Sorting list is: 10 23 35 45
How to sort ArrayList in descending order in Java :
in order to sort the list in decreasing order use Collections.reverseOrder() method along with Collections.sort(). In the below example we have used.
Collections.sort(arraylist, Collections.reverseOrder());
However the reverse order sorting can also be done by sorting list in ascending order first and then it will be reversed.
Collections.sort(list);
Collections.reverse(list);
Example :
package com.example;
import java.util.ArrayList;
import java.util.Collections;
public class ListSorting {
public static void main(String args[]) {
ArrayList<String> arraylist = new ArrayList<String>();
arraylist.add("A");
arraylist.add("Z");
arraylist.add("B");
arraylist.add("G");
/* ArrayList Element before sorting */
System.out.println("Before Sorting Element is:");
for (String str : arraylist) {
System.out.println(str);
}
/* Sorting list in decreasing order */
Collections.sort(arraylist, Collections.reverseOrder());
System.out.println("ArrayList element in descending order:");
for (String str : arraylist) {
System.out.println(str);
}
}
}
Output :
Before Sorting Element is: A Z B G ArrayList element in descending order: Z G B A
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