Several methods of flipping strings in java

For string processing problems, we often encounter problems that directly or indirectly need to flip (reverse) strings in the written test. Here are some methods (but not limited to):

Method 1: Use the toCharArray( ) method, then reverse the assignment

import java.util. *;
public class Test5{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            char[] c1 = sc.next().toCharArray();
            int len = c1.length;
            char[] c2 = new char[len];
            for(int i = 0; i < len; i ++){
                c2[i] = c1[len-1-i];
            }
            String res = new String(c2);
            System.out.println(res);
        }
    }
}

Method 2: Use the reverse( ) method of the StringBuilder class

import java.util.Scanner;
public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            System.out.println(new StringBuilder(sc.next()).reverse());
        }
    }
}

Method 3: If only consider the output, do not consider the return

import java.util.Scanner;
public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            String s = sc.next();
        	for(int i = s.length()-1; i >= 0; i--)
        		System.out.print(s.charAt(i));
        }
    }
}

Method 4: Use the static method reverse( ) of collections

import java.util. *;
public class Test5{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
        	/*
        	char[] c = sc.next().toCharArray();
        	List<Character> list = new ArrayList<Character>();
        	for(int i =0;i<c.length;i++)
        		list.add(c[i]);
        	Collections.reverse(list);
        	for(Character cha:list)
        		System.out.print(cha);
        		*/
        	String[] s = sc.nextLine().split("");
        	List<String> list = Arrays.asList(s);
        	Collections.reverse(list);
        	for(String s1:list)
        		System.out.print(s1);
        }
    }
}