如何在 Java 中将非常大的十进制数转换为二进制数

Here is a quik&dirty (very very very dirty) code:

public class BigDec2Bin {

    public static int[] string2arrayReversed( String s )
    {
        char a[] = s.toCharArray();
        int  b[] = new int[ s.length() ];
        for( int i = 0; i < a.length; i++ )
        {
            b[a.length-1-i] = a[i] - 48;
        }
        return b;
    }

    // adds two binary numbers represented as strings
    public static String add( String s1, String s2 )
    {
        String result = "", stmp;
        int[] a1, a2;
        int ctmp, mark = 0;

        // a1 should be the longer one
        a1 = string2arrayReversed( ( s1.length() > s2.length() ? s1 : s2 ) );
        a2 = string2arrayReversed( ( s1.length() < s2.length() ? s1 : s2 ) );

        for( int i = 0; i < a1.length; i++ )
        {
            ctmp = a1[i] + ( i < a2.length ? a2[i] : 0 ) + mark;

            switch( ctmp )
            {
                default:
                case 0:
                    stmp = "0";
                    mark = 0;
                    break;
                case 1:
                    stmp = "1";
                    mark = 0;
                    break;
                case 2:
                    stmp = "0";
                    mark = 1;
                    break;
                case 3:
                    stmp = "1";
                    mark = 1;
                    break;
            }

            result = stmp + result;
        }

        if( mark > 0 ) { result = "1" + result; }

        return result;
    }

    public static String dec2bin( String s )
    {
        String result = "";

        for( int i = 0; i < s.length() ; i++ )
        {
            result = add( result + "0", result + "000" );
            result = add( result, Integer.toBinaryString( s.charAt(i) - 48 ) );
        }

        return result;
    }

    public static void main( String[] args )
    {
        String dec = "12345"; // should be 11000000111001
        System.out.println( "dec2bin( " + dec + " ) = " + dec2bin( dec ) );

        dec = "12345678901234567890123456789012345678901234567890";
        System.out.println( "dec2bin( " + dec + " ) = " + dec2bin( dec ) );
    }

}

<小时>

输出:

dec2bin(12345) = 011000000111001

result = add( result + "0", result + "000" );

result = add( result, Integer.toBinaryString( s.charAt(i) - 48 ) );