Valid Parentheses | LeetCode | Java

Stack<Character> stack = new Stack<>();

for(char ch : s.toCharArray()){
if(stack.isEmpty())
stack.add(ch);
else if(!stack.isEmpty()){
if(ch==‘]’ && stack.peek()==‘[‘)
stack.pop();

else if(ch==‘}’ && stack.peek()==‘{‘)
stack.pop();

else if(ch==‘)’ && stack.peek()==‘(‘)
stack.pop();

else
stack.push(ch);
}
}

return stack.isEmpty();
}
}