self learning 2

Hash Map - NSDictionary like mapping but with generic types
Stack - simple enough that is data structure of stack

the following code is java implementation of using stack to check the code syntax are properly closed.

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import java.util.*; class SyntaxTester { private HashMap<String, String> mapping; public SyntaxTester() { mapping = new HashMap<String, String>(); mapping.put("(", ")"); mapping.put("[", "]"); mapping.put("{", "}"); } public void check(String input) { Stack<String> stack = new Stack<String>(); for (int i = 0 ; i < input.length() ; i++ ) { String currentString = input.substring(i, i+ 1) ; //opener if ( mapping.keySet().contains(currentString) ) { stack.add(currentString); } //closer else if (mapping.containsValue(currentString)) { //get last stack element String lastElement = stack.peek(); if (mapping.get(lastElement).equals(currentString) ) { stack.pop(); } } } if (stack.empty()) { System.out.println("input : " + input + " is valid."); } else { System.out.println("input : " + input + " is not valid."); } } } class HashMapDemo { public static void main(String[] args) { String input = "{[]()}"; SyntaxTester tester = new SyntaxTester(); if (args.length > 0) { tester.check(args[0]); } else { tester.check(input); } } }