配列の構文:
Arrays.sort(array_name);
コレクション用
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Collections.sort(array_name_list);
次の点は次のとおりです:
以下に、Java での並べ替えで並べ替えを実行できる方法のいくつかを示します。
これは、配列全体を昇順で並べ替えるのに使用されます。デフォルトでは、このメソッドは配列要素を昇順に並べ替えます。
コード:
import java.util.Arrays;
public class SimpleSort
{
public static void main(String[] args)
{
//Unsorted array of numbers
Integer[] arr = new Integer[] {100, 20, 10, 30, 80, 70, 90, 40, 50, 60};
//Sort function to sort the above array
Arrays.sort(arr);
//Printing the sorted array on console
System.out.println(Arrays.toString(arr));
}
}出力:
Java のこのメソッドは、配列を逆順または降順にソートするために使用されます。要素を降順に並べ替える必要があるシナリオがあり、Java は組み込みメソッドを通じてそれを行います。
コード:
import java.util.Arrays;
public class ReverseSort
{
public static void main(String[] args)
{
//Unsorted array of numbers
Integer[] arr = new Integer[] { 100, 20, 10, 30, 80, 70, 90, 40, 50, 60};
//Sort function to sort the above array
Arrays.sort(arr, Collections.reverseOrder());
//Printing the sorted array on console
System.out.println(Arrays.toString(arr));
}
}出力:
配列全体ではなく配列の一部をソートする必要がある場合、Java は 3 つのパラメータ (配列名、ソートを開始する必要がある最初のインデックス) を指定してこのタイプの配列をソートする機能を提供します。ソートが必要になるまでの最後のインデックス。
コード:
import java.util.Arrays;
public class ReverseSort
{
public static void main(String[] args)
{
//Unsorted array of numbers
Integer[] arr = new Integer[] { 100, 20, 10, 30, 80, 70, 90, 40, 50, 60};
//Sort function to sort the above array
Arrays.sort(arr, 1, 5);
//Printing the sorted array on console
System.out.println(Arrays.toString(arr));
}
}出力:
From Java 8, the new API of the parallel sort has been released. Basically, in Parallel sort, the array is divided into 2 sub-arrays, and then the basic Array.sort() function is performed by a separate thread. The sorted arrays are then merged in the end to form the fully sorted array. This is done to leverage the use of multi-threading.
Code:
import java.util.Arrays;
public class ParallelSort
{
public static void main(String[] args)
{
//Unsorted array of numbers
Integer[] arr = new Integer[] { 100, 20, 10, 30, 80, 70, 90, 40, 50, 60};
//parallel Sort function to sort the above array
Arrays.parallelSort(arr);
//Printing the sorted array on console
System.out.println(Arrays.toString(arr));
}
}Output:
Like a normal Array.sort(), Arrays.parallelSort() also provides the facility to sort a particular range of array or sorting an array in reverse order.
Syntax:
// to Sort a range of array by parallelsort Arrays.parallelSort(array_name, findex, lindex); // to sort an array in reverse order using parallelSort Arrays.parallelSort(array_name, Collections.reverseOder());
This method is used to sort the collections like list, map, Set, etc. It uses the merge sort and gives the same complexity as Array.sort(), i.e. O(n(logn)).
Code:
import java.util.Arrays;
import java.util.Collections;
public class ListSort
{
public static void main(String[] args)
{
//Unsorted list
Integer[] arr = new Integer[] { 100, 20, 10, 30, 80, 70, 90, 40, 50, 60 };
List<Integer> arrList = Arrays.asList(arr);
//Sorting of list using the method
Collections.sort(arrList);
//Printing the list sorted above
System.out.println(arrList);
}
}Output:
Code:
import java.util.Arrays;
import java.util.Collections;
public class ListSortRev
{
public static void main(String[] args)
{
//Unsorted array list of Integers
Integer[] arr = new Integer[] {100, 20, 10, 30, 80, 70, 90, 40, 50, 60 };
List<Integer> arrList = Arrays.asList(arr);
//Sorting of list using the method
Collections.sort(arrList);
//Printing the list sorted above
System.out.println(arrList);
}
}Output:
There are 3 basic rules while sorting a collection ‘Set’ using the above method sort(array_name):
Code:
List<Integer> numList = new ArrayList<Integer>(num) ; //Sorting the list retrieved above Collections.sort(numList); // Converting sorted List into Set num = new LinkedHashSet<>(numList); //Printing the Resulting Set on console System.out.println(num); } }
Output:
Collection Map in Java is a combination of key and value So sorting can be done both ways, either through key or by value.
Code:
import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
public class SortHashKey
{
public static void main(String[] args)
{
HashMap<Integer, String> map = new HashMap<>();
map.put(80, "Akshay");
map.put(20, "Akash");
map.put(10, "Bob");
map.put(30, "Nitika");
map.put(90, "Yashi");
map.put(100, "Dragisa");
TreeMap<Integer, String> treeMap = new TreeMap<>(map);
System.out.println(treeMap);
}
}Output:
One of the easiest ways to sort the elements of the Map by Keys is by adding the unsorted map elements in the TreeMap. TreeMap automatically sorts the elements in the ascending order of Hash Keys. Though collection.sort() can also be used to do the same, it is somewhat complex and needs to be coded well.
Code:
import java.util.HashMap;
import java.util.Map;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.Map;
public class SortHashValue
{
public static void main(String[] args)
{
HashMap<Integer, String> map = new HashMap<>(); map.put(80, "Akshay");
map.put(20, "Akash");
map.put(10, "Bob");
map.put(30, “Nitika");
map.put(90, "Yashi");
map.put(100, "Dragisa");
LinkedHashMap<Integer, String> sorted = new LinkedHashMap<>(); map.entrySet()
.stream()
.sorted(Map.Entry.comparingByValue())
.forEachOrdered(x -> sorted.put(x.getKey(), x.getValue()));Output:
In the above example of sorting of Map by value, firstly we set the entries using the map.entrySet() and then stream of those entries using stream() method, call the sorted array using sorted() method by comparing by value in the pair. for each ordered() is used to traverse the stream to produce the result.
Comparable is an Interface, and it makes the classes comparable to its instances.
To compare the two instances of the same class, Comparable interface needs to be implemented, and the method compareTo() needs to be overridden. The classes that implement this interface, its list of objects are sorted automatically using the method Collections.sort() and Arrays.sort().
Code:
ArrayList<Employee> list = new ArrayList<>(); // Adding the instance objects of class Employee in list list.add(new Employee(10, "Akshay"))); list.add(new Employee(40, "Bob"))); list.add(new Employee(20, "Priyansh"))); list.add(new Employee(50, "Chandni"))); list.add(new Employee(70, "Yashi"))); Collections.sort(list); // Printing the sorted list on Console System.out.println(list);
Output:
The Sorting in Java methods used in Java for multiple scenarios of Arrays and Collections are explained above. A programmer needs to keep in mind how the sort() method should be used for different Collection types. With Java 8, sorting can also be done through Lambdas to implement the Comparator interface, which makes the sorting easier. Though it is a bit difficult to learn all of them, it can be easy working with them if all the basic concepts of Java, especially data streaming, Arrays, and Collections, are clear. Though sorting Algorithms are evergreen and can be easily implemented in Java-like other programming languages, they have varying complexity, and the in-built function sort() of Java makes things easier if the basic concepts are learned by heart.
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