先说下整体思路:
包含小数的十六进制,我们可以先把它分为整数和小数两部分,
然后在进行字符串比较,进行相应的替换。

包含二进制的小数,思路差不多,需要注意的是左边整数不够四位的补0,右边也如此。

import java.math.BigDecimal;

public class Test13 {

    public static void main(String[] args) {//十六-二
        // TODO 自动生成的方法存根

        String e = "0.77";
        String num1 = "";
        String num2 = "";
        if(e.indexOf(".")==-1)//这里进行判断是否是小数
        {
            num1 = e;
            num2 = "0";
        }
        else
        {
            String[] s1 = e.split("\\.");//把小数分成两部分
            num1 = s1[0];
            num2 = s1[1];
        }

        System.out.println("整数为:"+num1);
        System.out.println("小数为:"+num2);

        String a1= "";
        String a3= "";
        String a2 = "";//最后输出

        int i = 0, i1 = 0;
        int j1 = 0;
        String[] ej={"0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111"};
        String[] bj={"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"};


        //处理整数
        if(num1.equals("0"))
        {
            a1 = "0";
        }
        else{
        j1 = num1.length();
        i1 = 0;
            for(i = 0; i<j1;i++)
            {

                for(int j = 0; j<ej.length;j++)
                {
                    System.out.println("截取的值:"+num1.substring(i1, i1+1));


                    if(num1.substring(i1, i1+1).equals(bj[j]))
                    {
                        System.out.println("j的值"+j);
                        a1 =a1+ ej[j];
                        i1 = i1 +1;
                        break;

                    }
                }


            }
            System.out.println("整数十六进制转二进制为:"+a1);
        }

        //小数部分
            if(num2.equals("0"))
            {
                a2 = a1;
            }
            else
            {

            j1 = num2.length();//计算循环次数
            System.out.println(j1);
            i1 =0;
            for(i = 0; i<j1;i++)
            {

                //ej2[i]=num1.substring(i, i+2);
                for(int j = 0; j<ej.length;j++)
                {
                    System.out.println("截取的值:"+num2.substring(i1, i1+1));

                    if(num2.substring(i1, i1+1).equals(bj[j]))
                    {
                        System.out.println("j的值"+j);
                        a3 =a3+ ej[j];
                        i1 = i1 +1;

                        break;

                    }
                }


            }

            System.out.println("小数十六进制转二进制为:"+a3);
            a2 = a1+"."+a3;
            }
            System.out.println("十六进制转二进制为:"+a2);



    }
}
//上面就是大部分代码了,八进制转二进制也是同样的道理

接下来我们看看二进制转十六进制:

String s = "100001.01"
double s = Double.valueOf(e);
                        String num1 =String.valueOf((int)s);//整数
                        int zj1 = (int) s;
                        BigDecimal b1 = new BigDecimal(e);
                        BigDecimal b2 = new BigDecimal(zj1);
                        double zj2 = b1.subtract(b2).doubleValue();//小数部分
                        String num0 = String.valueOf(zj2);
                        //如果没有小数点,直接使用split就会报错。。
                        String[] s1 = num0.split("\\.");

                        String num2 = s1[1];//直接取小数

                        System.out.println("整数为:"+num1);
                        System.out.println("小数为:"+num2);

                        String a1= "";
                        String a3= "";
                        //String a2 = "";//最后输出

                        int i = 0, i1 = 0;
                        int j1 = 0;
                        String[] ej={"0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111"};
                        String[] bj={"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"};

                        if(num1.equals("0"))
                        {
                            a1 = "0";
                        }

                        else
                        {

                        //处理整数
                        if((num1.length()%4)!=0)
                        {
                             j1 = 4-num1.length()%4;
                            for(i = 0;i<j1;i++)
                            {
                                num1 = "0"+num1;

                            }
                            System.out.println("补零   "+num1);//计算左边需要补几个0
                        }

                        j1 = num1.length()/4;
                        System.out.println(j1);
                        for(i = 0; i<j1;i++)
                        {

                            //ej2[i]=num1.substring(i, i+2);
                            for(int j = 0; j<ej.length;j++)
                            {
                                System.out.println("截取的值:"+num1.substring(i1, i1+4));

                                if(num1.substring(i1, i1+4).equals(ej[j]))
                                {
                                    System.out.println("j的值"+j);
                                    a1 =a1+ bj[j];
                                    i1 = i1 +4;
                                    break;

                                }
                            }


                        }
                        System.out.println("整数二进制转十六进制为:"+a1);
                        }

                        if(num2.equals("0"))
                        {
                            a2 = a1;
                        }
                        else
                        {
                        //小数部分
                        if((num2.length()%4)!=0)
                        {
                             j1 = 4-num2.length()%4;//需要添加几个0
                            for(i = 0;i<j1;i++)
                            {
                                num2 = num2+"0";//这里和整数的不同

                            }
                            System.out.println("补零   "+num2);
                        }

                        j1 = num2.length()/4;//计算循环次数
                        System.out.println(j1);
                        i1 =0;
                        for(i = 0; i<j1;i++)
                        {

                            //ej2[i]=num1.substring(i, i+2);
                            for(int j = 0; j<ej.length;j++)
                            {
                                System.out.println("截取的值:"+num2.substring(i1, i1+4));

                                //System.out.println(num1.substring(i, i+3));
                                //System.out.println("ej[j]的值:"+ej[j]);
                                //System.out.println(num1.substring(i, i+3).equals(ej[j]));


                                if(num2.substring(i1, i1+4).equals(ej[j]))
                                {
                                    System.out.println("j的值"+j);
                                    a3 =a3+ bj[j];
                                    i1 = i1 +4;

                                    break;

                                }
                            }


                        }

                        System.out.println("小数二进制转十六进制为:"+a3);
                        a2 = a1+"."+a3;
                        }
                        System.out.println("二进制转十六进制为:"+a2);

                    }

haha,上面比较乱,我好久之前写的了,没时间整理,处理整数和小数哪里有优化的地方,或许是当时想复杂了,将就着看吧。新手java小白的心得,有不足的地方,可以指点一二。不要和我说你怎么不用函数。。非要搞这么复杂,哈哈。八二和二八转换也和上面差不多