Java implements an array inversion method instance

The method of array flip (java implementation), array flip, is to invert the array, for example, the original array is: {"a","b","c","d"}, then the flipped array is {"d","c","b","a"}.

[Method 1] Use a collection of tool classes: Collections. reverse(ArrayList) to reverse the array:

import java.util.ArrayList;import java.util.Collections; 
public class Main { 
  public static void main(String[] args) { 
   ArrayList arrayList = new ArrayList(); 
   arrayList.add("A"); 
   arrayList.add("B"); 
   arrayList.add("C"); 
   arrayList.add("D"); 
   arrayList.add("E"); 
   System.out.println(" Pre-reverse sort : " + arrayList); 
   Collections.reverse(arrayList); 
   System.out.println(" Reverse sort : " + arrayList); 
  } 
} 

The output result of the above code operation is:

Sort before reversal: [A, B, C, D, E]
Reverse ordering: [E, D, C, B, A]

[Method 2] Use the set ArrayList to implement inversion:

[Method 3] Invert the array directly, that is, the first element of the inverted array is equal to the last element of the source array:

The implementation codes for methods 2 and 3 are as follows:

package javatest2; 
 
import java.util.ArrayList; 
 
public class JavaTest2 { 
 
  public static void main(String[] args) { 
    String[] Array = { "a", "b", "c", "d", "e" }; 
    reverseArray1(Array);//  Using the collection ArrayList Implement reverse  
    for (int j = 0; j < Array.length; j++) { 
      System.out.print(Array[j] + " "); 
    } 
 
    System.out.print("\n"); 
    String[] temp = reverseArray2(Array);//  Invert directly using an array  
    for (int j = 0; j < temp.length; j++) { 
      System.out.print(Array[j] + " "); 
    } 
 
  } 
 
  /* 
   *  Function: reverseArray1 and reverseArray2 
   *  Function: Implementation   The array to flip  
   *  Such as: {'a','b','c','d'} become {'d','c','b','a'} 
   */ 
  private static void reverseArray1(String[] Array) { 
    ArrayList<String> array_list = new ArrayList<String>(); 
    for (int i = 0; i < Array.length; i++) { 
      array_list.add(Array[Array.length - i - 1]); 
    } 
    Array = array_list.toArray(Array); 
  } 
 
  private static String[] reverseArray2(String[] Array) { 
    String[] new_array = new String[Array.length]; 
    for (int i = 0; i < Array.length; i++) { 
      //  Inverted array of the first 1 The elements are equal to the end of the source array 1 An element:  
      new_array[i] = Array[Array.length - i - 1]; 
    } 
    return new_array; 
  } 
 
}