Approach-1
  
 Source Code
  

    
// Contributed by - Anuj Das ( GC College, Silchar - @ Department of Computer Science )
import java.util.Scanner;

class BinToDec {

    public static void main(String[ ] args) {
        System.out.print("Enter a Binary Number:  ");
        String binary = new Scanner(System.in).next();
        System.out.println("Equivalent Decimal Number: " + Integer.parseInt(binary , 2));
    }
}

    

cmd->  javac  BinToDec.java
cmd->  java  BinToDec

Enter a Binary Number:  101011
Equivalent Decimal Number: 43

    
Approach-2
  
 Source Code
  

    
// Contributed by - Anuj Das ( GC College, Silchar - @ Department of Computer Science )
import java.lang.Math;
import java.util.Scanner;

class BinaryToDecimal {
  static int convertToDec(String bin) {
      int[] binArray = new int[1024];
      int eqv_dec = 0;
  
      for (int i = bin.length() - 1; i >= 0; i--) {
          binArray[i] = Character.getNumericValue(bin.charAt(i));
      }

      for (int i = 0; i < bin.length(); i++) {
          if (binArray[i] == 1) 
              eqv_dec += (int)Math.pow(2, bin.length()-1 - i);
          else
              continue;
      }
      return eqv_dec;
  }

  // Driver Code!
  public static void main(String[] args) {
      System.out.print("Enter Binary Number:  ");
      String bin = new Scanner(System.in).next();
      System.out.println("Given Binary: " + bin);
      int eqv_dec = convertToDec(bin);
      System.out.println("Equivalent Decimal Number: " + eqv_dec);
  }
}

    

cmd->  javac  DecimalToBinary.java
cmd->  java  DecimalToBinary

Enter Binary Number:  101010110
Given Binary: 101010110
Equivalent Decimal Number: 342