2. Replace spaces JAVA

Offer to prove safety

Please implement a function, a string to replace each space to "20%." For example, when the string is We Are Happy. After the string is replaced after We% 20Are% 20Happy.

replaceSpace与replaceSpace2两种方法。

import java.util.Arrays;

public class Space {
    public static void main(String[] args) {
        StringBuffer s = new StringBuffer("sda sad aa123");
        String res  = replaceSpace2(s);
        System.out.println(res);
    }

    public static String replaceSpace(StringBuffer str) {
        if (str == null) {
            return "";
        }
        String ss = new String();
        ss.charAt(1);
        ss = str.toString().replace( " " , "%20" );
        return ss;
    }
    
    public static String replaceSpace2(StringBuffer str) {
        if (str == null) {
            return "";
        }
        int black;
        black = 0;
        char[] chars = str.toString().toCharArray();
        for(int i=0;i<chars.length-1;i++){
            if(chars[i] == ' '){
                black++;
            }
        }
        char[] new_chars = new char[str.length()+2*black];
        int num;
        int num2;
        num = str.length()+2*black-1;
        num2 = str.length()-1;
        while(num2>=0){
            if(chars[num2] == ' '){
                new_chars[num--] = '0';
                new_chars[num--] = '2';
                new_chars[num--] = '%';
                num2--;
            }
            else {
                new_chars[num--] = chars[num2--];
            }
        }
        String ss = String.valueOf(new_chars);
        return ss;
    }
}