{"id":18832,"date":"2022-11-02T02:53:08","date_gmt":"2022-11-01T21:23:08","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-how-to-parse-an-input-string-such-as-41-resolve-the-expression-and-return-boolean-duplicate\/"},"modified":"2022-11-02T02:53:08","modified_gmt":"2022-11-01T21:23:08","slug":"solved-how-to-parse-an-input-string-such-as-41-resolve-the-expression-and-return-boolean-duplicate","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-how-to-parse-an-input-string-such-as-41-resolve-the-expression-and-return-boolean-duplicate\/","title":{"rendered":"[Solved] how to parse an input string such as &#8220;4>1&#8221;, resolve the expression and return boolean [duplicate]"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-45730477\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"45730477\" data-parentid=\"45728846\" data-score=\"3\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<h1>There is no easy answer<\/h1>\n<p>For starters there are no easy solutions. I noticed somebody mentioning <code>Boolean.valueOf(...)<\/code>;<\/p>\n<p>The goal of the <code>Boolean.valueOf(String)<\/code> method is not to evaluate conditions or equations. It is just a simple method to convert a <code>String<\/code> with value <code>\"true\"<\/code> or <code>\"false\"<\/code> to a <code>Boolean<\/code> object.<\/p>\n<p>Anyway, if you want this kind of functionality, you have to set some clear limitations. <em>(note: some equations have no answer: &#8220;0\/0 = 0\/0&#8221;)<\/em><\/p>\n<h1>Regex parsing<\/h1>\n<p>If you are simply comparing integers with integers, then you could assume that the equations will always be in the following format:<\/p>\n<pre><code>&lt;integer1&gt;[whitespace]&lt;operator&gt;[whitespace]&lt;integer2&gt;\n<\/code><\/pre>\n<p>Then, what you could do, is split your string in 3 parts using a regular expression.<\/p>\n<pre><code>public static boolean evaluate(String input)\n{\n  Pattern compile = Pattern.compile(\"(\\\\d+)\\\\s*([&lt;&gt;=]+)\\\\s*(\\\\d+)\");\n  Matcher matcher = compile.matcher(input);\n  if (matcher.matches())\n  {\n    String leftPart = matcher.group(1);\n    String operatorPart = matcher.group(2);\n    String rightPart = matcher.group(3);\n\n    int i1 = Integer.parseInt(leftPart);\n    int i2 = Integer.parseInt(rightPart);\n\n    if (operatorPart.equals(\"&lt;\")) return i1 &lt; i2;\n    if (operatorPart.equals(\"&gt;\")) return i1 &gt; i2;\n    if (operatorPart.equals(\"=\")) return i1 == i2;\n    if (operatorPart.equals(\"&lt;=\")) return i1 &lt;= i2;\n    if (operatorPart.equals(\"&gt;=\")) return i1 &gt;= i2;\n\n    throw new IllegalArgumentException(\"invalid operator '\" + operatorPart + \"'\");\n  }\n\n  throw new IllegalArgumentException(\"invalid format\");\n}\n<\/code><\/pre>\n<h1>Script Engines<\/h1>\n<p>Java also supports script engines (e.g. Nashorn and others). These engines can call javascript methods, such as the <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/www.w3schools.com\/jsref\/jsref_eval.asp\"><code>eval(...)<\/code><\/a> javascript method, which is exactly what you need. So, this is probably a better solution.<\/p>\n<pre><code>public static boolean evaluate(String input)\n{\n  try\n  {\n    ScriptEngine engine = new ScriptEngineManager().getEngineByName(\"nashorn\");\n    Object result = engine.eval(\"eval('\" + input + \"');\");\n    return Boolean.TRUE.equals(result);\n  }\n  catch (ScriptException e)\n  {\n    throw new IllegalArgumentException(\"invalid format\");\n  }\n}\n<\/code><\/pre>\n<p>This solution can handle more complicated input, such as <code>\"!(4&gt;=10)\"<\/code>.<\/p>\n<p><em>Note: for security reasons, you may want to strip specific characters from the user input. (e.g. the <code>'<\/code> character)<\/em><\/p>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\"><\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved how to parse an input string such as &#8220;4>1&#8221;, resolve the expression and return boolean [duplicate] <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] There is no easy answer For starters there are no easy solutions. I noticed somebody mentioning Boolean.valueOf(&#8230;); The goal of the Boolean.valueOf(String) method is not to evaluate conditions or equations. It is just a simple method to convert a String with value &#8220;true&#8221; or &#8220;false&#8221; to a Boolean object. Anyway, if you want this &#8230; <a title=\"[Solved] how to parse an input string such as &#8220;4&gt;1&#8221;, resolve the expression and return boolean [duplicate]\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-how-to-parse-an-input-string-such-as-41-resolve-the-expression-and-return-boolean-duplicate\/\" aria-label=\"More on [Solved] how to parse an input string such as &#8220;4&gt;1&#8221;, resolve the expression and return boolean [duplicate]\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[908,323,380,362],"class_list":["post-18832","post","type-post","status-publish","format-standard","hentry","category-solved","tag-boolean-expression","tag-java","tag-parsing","tag-string"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.4 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>[Solved] how to parse an input string such as &quot;4&gt;1&quot;, resolve the expression and return boolean [duplicate] - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-how-to-parse-an-input-string-such-as-41-resolve-the-expression-and-return-boolean-duplicate\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] how to parse an input string such as &quot;4&gt;1&quot;, resolve the expression and return boolean [duplicate] - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] There is no easy answer For starters there are no easy solutions. 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