字符串十六进制二进制（java）

Question

    public class Try{
        public static void main(String args[]){
            String hex="11000010111100001001111010111000";
             String HexaBin="";
                for (int i = 0; i < hex.length(); i+=4) {
                    String str = hex.substring(i, i+4);
                    if (str=="0000")
                        HexaBin+= "0";
                    else if (str=="0001")
                        HexaBin+="1";
                    else if(str=="0010")
                        HexaBin+="2";
                    else if(str=="0011")
                        HexaBin+="3";
                    else if(str=="0100")
                        HexaBin+="4";
                    else if(str=="0101")
                        HexaBin+="5";
                    else if(str=="0110")
                        HexaBin+="6";
                    else if(str=="0111")
                        HexaBin+="7";
                    else if(str=="1000")
                        HexaBin+="8";
                    else if(str=="1001")
                        HexaBin+="9";
                    else if(str=="1010")
                        HexaBin+="A";
                    else if(str=="0000")
                        HexaBin+="B";
                    else if(str=="1100")
                        HexaBin+="C";
                    else if(str=="1101")
                        HexaBin+="D";
                    else if(str=="1110")
                        HexaBin+="E";
                    else if(str=="1111")
                        HexaBin+="F";

                }
                   System.out.println(HexaBin);
            }
        }

I have a string containing binary numbers. I need to convert it to Hexadecimal without using any built in function. I tried these codes but it wont run. I don't know why.

When I run it, it gets terminated. what's the problem with these codes.

Answer 1

use String.equals() instead of ==

if (str.equals("0000"))
  HexaBin+= "0";
else if (str.equals("0001"))
  HexaBin+="1";
...

Another point : it will not make you program fail but it is a bad practice to concatene Strings like this :

 HexaBin+="5";

You should rather declare your HexaBin as a StringBuilder and call StringBuilder.append():

//btw, variable names should begin with a lower case character.
StringBuilder hexaBin = new StringBuilder();
...
hexaBin.append("5");

Answer 2

Replace all == with the equals method in your if statements.

The == operator checks whether the references to the objects are equal or not while the equals method checks the actual contents.

Answer 3

Here is a different approach which may be interesting for you own use, but no professor will believe you wrote ;)

String hex = "11000010111100001001111010111000";
// to long
long val = 0;
for (char ch : hex.toCharArray())
    val = val * 2 + ch - '0';
String hexidecimal = "0123456789ABCDEF";
for (int i = (hex.length() - 1) / 4 * 4; i >= 0; i -= 4)
    System.out.print(hexidecimal.charAt((int) ((val >>> i) & 0xF)));
System.out.println();

prints

62F09EB8

Answer 4

String is object in java so use equals() Instead of ==

so Change to

if (str.equals("0000")) // for all cases

Answer 5

使用equals()比较两个String是否equality因为String是reference类型。

Answer 6

As the other posters alredy said, compare Strings with equals() , not with == .

Furthermore, you have a copy-paste-error in your code, "B" will never printed as you compare it with 0000 instead of 1011 .

If you want to convert numbers between different radices, it's easier to use the functions on the number classes .

String hex = "11000010111100001001111010111000";

long num = Long.parseLong(hex, 2);
String hexaBin = Long.toString(num, 16).toUpperCase();