Valid Parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

public boolean isValid(String s) {
        Stack<Character> stack = new Stack<>();
        if (s.length()==0){
            return true;
        }
        int len = s.length();
        for (int i=0;i<len;i++){
            switch (s.charAt(i)){
                case '(':{
                    stack.push('(');
                    break;
                }
                case '{':{
                    stack.push('{');
                    break;
                }
                case '[':{
                    stack.push('[');
                    break;
                }
                case ')':{
                    if (!stack.empty()&&stack.peek()=='('){ //判断是否为空不然有异常
                        stack.pop();
                        break;
                    }else{
                        return false;
                    }
                }
                case '}':{
                    if (!stack.empty()&&stack.peek()=='{'){
                        stack.pop();
                        break;
                    }else{
                        return false;
                    }
                }
                case ']':{
                    if (!stack.empty()&&stack.peek()=='['){
                        stack.pop();
                        break;
                    }else{
                        return false;
                    }
                }
                default:break;
            }
        }
        if (stack.empty()){
            return true;
        }else{
            return false;
        }
    }