Reverse Integer

public class Solution {
    public int reverse(int x) {
        
        if(x == 0){
            return 0;
        }
        
        String result = "";
        String flag = "";
        if(x<0){
            flag = "-";
        }
        ArrayList<String> list = new ArrayList<String>();
        while(x != 0){
            int temp = x%10;
            list.add(temp+"");
            x = x/10;
        }
       
        for(String e:list){
            result+=e;
        }
        
        result=flag+result.replace("-","");
        
        if(Double.valueOf(result)>Math.pow(2,31)-1||Double.valueOf(result)<-Math.pow(2,31)){
            return 0;
        }
        
        return Integer.valueOf(result);
        
    }
}

public class Solution {
    public int reverse(int x) {
        String s = x+"";
        char[] char_array = s.toCharArray();
        int size = char_array.length;
        String re = "";
        for(int i=0;i<size;i++){
            re=re+char_array[size-i-1];
        }
        
        if(x<0){
            re="-"+re.replace("-","");
        }
        
        if(Double.valueOf(re)>Math.pow(2,31)-1||Double.valueOf(re)<-Math.pow(2,31)){
            return 0;
        }
        
        return Integer.valueOf(re);
        
    }
}