Why is bufferedreader not working in Java code example

Example 1: bufferedreader java

import java.io.BufferedReader;
//
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
System.out.println(reader.readLine());

Example 2: bufferedreader in java

class Main {
	public static void main (String[] args) throws IOException{
                      
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] str = br.readLine().split(" ");      // 6 2
		String[] input = br.readLine().split(" ");   // 1 2 3 4 5 6


		int n = Integer.parseInt(str[0]);  // 6
		int k = Integer.parseInt(str[1]);  // 2

		
      	int [] arr = new int [n];
		
      	for(int i=0; i<n; i++) 
		{
         arr[i] = Integer.parseInt(input[i]);  // 1 2 3 4 5 6
        }
	  
	  
	}
}

Example 3: java bufferedreader

private static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
private static StringTokenizer st;
static String next() throws IOException {
    while (st==null||!st.hasMoreTokens()) {
        st = new StringTokenizer(br.readLine().trim());
    }
    return st.nextToken();
}
static long readLong() throws IOException {
    return Long.parseLong(next());
}
static int readInt() throws IOException {
    return Integer.parseInt(next());
}
static double readDouble() throws IOException {
    return Double.parseDouble(next());
}
static String readLine() throws IOException {
    return br.readLine().trim();
}