ExperimentBox/app/src/main/java/ch/nuth/zhaw/exbox/BracketServer.java

package ch.nuth.zhaw.exbox;

import java.util.HashMap;
import java.util.Map;
import java.util.regex.MatchResult;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class BracketServer implements CommandExecutor {
    private static Pattern bracketPattern = Pattern.compile("(/\\*|\\*/|[(){}\\[\\]<>])");

    private static Map<String, String> bracketPairs;

    public BracketServer() {
        super();

        bracketPairs = new HashMap<>() {
            {
                put("(", ")");
                put("[", "]");
                put("{", "}");
                put("<", ">");
                put("/*", "*/");
            }
        };
    }

    @Override
    public String execute(String command) throws Exception {
        return Boolean.toString(checkBrackets(command)) + "\n";
    }

    public boolean checkBrackets(String expression) {
        ListStack openBrackets = new ListStack();
        Matcher matcher = bracketPattern.matcher(expression);
        Iterable<MatchResult> results = () -> matcher.results().iterator();

        for (MatchResult result : results) {
            if (bracketPairs.keySet().contains(result.group())) {
                openBrackets.push(result.group());
            } else if (!openBrackets.isEmpty() &&
                    result.group().equals(bracketPairs.get(openBrackets.peek()))) {
                openBrackets.pop();
            } else {
                return false;
            }
        }

        return openBrackets.isEmpty();
    }
}