blocks|key|4164185|text|这是Boolean.parseBoolean的源代码|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4164186|public+static+boolean+parseBoolean(String+b)+
{
++return+"true".equalsIgnoreCase(b)+?+true+:+false;
}|code-block|syntax|javascript|4164187|此函数唯一返回true的情况是传递给它的字符串为"true“(尽管大小写)。|4164188|如果要检查字符串是否是非空的，请使用String.isEmpty方法。如果你想真正“评估”字符串，那就不是那么简单了……但是你可能想通读一下Is+there+an+eval()+function+in+Java?。|4164189|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/2605032/is-there-an-eval-function-in-java^0|2|K|0|0|7|4|0|I|E|1Y|10|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@$9|16|A|17|1|18]]|E|$]]|$1|O|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

This is the source code for <code>Boolean.parseBoolean</code>:

<pre><code>public static boolean parseBoolean(String b) 
{
 return "true".equalsIgnoreCase(b) ? true : false;
}
</code></pre>

The only time this function returns <code>true</code> is if the string passed to it is either "true" (case notwithstanding).

If you're looking to check whether the string is non-empty, use the <code>String.isEmpty</code> method. If you're looking to actually "eval" the string, that isn't as straightforward... but you may want to read through <a href="https://stackoverflow.com/questions/2605032/is-there-an-eval-function-in-java">Is there an eval() function in Java?</a>.

blocks|key|4164797|text|您应该直接计算表达式，而不是在字符串中计算。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4164798|boolean+a,b,c;
a=true;
b=true;
c=true;
boolean+z=+(a%5Eb)%7Cc;
System.out.println(z);|code-block|syntax|javascript|4164799|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You should evaluate the expression directly not within the String. 

<pre><code>boolean a,b,c;
a=true;
b=true;
c=true;
boolean z= (a^b)|c;
System.out.println(z);
</code></pre>

blocks|key|4164259|text|在Java语言中，parseBoolean方法将字符串参数解析为布尔值。如果字符串参数不为空，并且忽略大小写，等于字符串“true”，则返回的布尔值表示值true。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4164260|因此，如果解析"(a%5Eb)%7Cc"，您将得到false，因为它不会计算表达式。|4164261|entityMap^0|9|C|1O|6|0|7|9|L|5|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|I|$]]

In Java, the <code>parseBoolean</code> method parses the string argument as a boolean. The boolean returned represents the value true if the string argument is not null and is equal, ignoring case, to the string <code>“true”</code>.

So, if you parse <code>"(a^b)|c"</code> you will get <code>false</code> as it's not going to evaluate the expression.

blocks|key|4164969|text|如果要计算表达式"(a%5Eb)%7Cc"的结果，其中a、b和c是上面定义的变量，只需像其他答案中所述那样直接作为java代码执行表达式即可。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4164970|boolean+result+=+(a%7Cb)%5Ec;|code-block|syntax|javascript|4164971|然而，如果你真的想要计算一个来自String的表达式，比如字符串来自用户输入，那么有一个名为JExl的库可以让你这样做：|4164972|http://commons.apache.org/proper/commons-jexl/|4164973|将以下代码行添加到maven+pom.xml中|4164974|<dependency>
++<groupId>org.apache.commons</groupId>
++<artifactId>commons-jexl3</artifactId>
++<version>3.1</version>
</dependency>|4164975|还没有测试下面的代码，但是你可以试一试。|4164976|import+org.apache.commons.jexl3.*;

JexlEngine+jexl+=+new+JexlBuilder().create();
String+expression+=+"(a%7Cb)%5Ec";
JexlExpression+jExpression+=+jexl.createExpression(expression);

//+JexlContext+stores+the+values+for+variables+used+in+an+JexlExpression
JexlContext+context+=+new+MapContext();
context.set("a",+true);
context.set("b",+true);
context.set("c",+true);

//+evaluate+expression.
Long+result+=+(Long)+jExpression.evaluate(context);
System.out.println(result);+//+0+for+false|4164977|当然，性能会比直接执行代码差，因为表达式必须解析到抽象语法树(AST)中才能进行计算。|4164978|entityMap|0|LINK|mutability|MUTABLE|url^0|8|9|N|1|P|1|R|1|0|0|G|6|0|0|1A|0|0|F|7|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1E|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1F|8|@$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1I|8|@]|D|@$9|1J|A|1K|1|1L]]|E|$]]|$1|O|3|P|5|6|7|1M|8|@$9|1N|A|1O|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1P|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|1Q|8|@]|D|@]|E|$]]|$1|U|3|V|5|H|7|1R|8|@]|D|@]|E|$I|J]]|$1|W|3|X|5|6|7|1S|8|@]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|1T|8|@]|D|@]|E|$]]]|Z|$10|$5|11|12|13|E|$14|N]]]]

If you want to evaluate the result of the expression <code>"(a^b)|c"</code> where <code>a</code>, <code>b</code>, and <code>c</code> are the variables defined above, just execute the expression directly as java code as stated in other answers.

<pre><code>boolean result = (a|b)^c;
</code></pre>

However, if one really wants to evaluate a an expression coming from a <code>String</code>, say when the string comes from user input, then there is a library called JExl that let's you do this:

<a href="http://commons.apache.org/proper/commons-jexl/" rel="nofollow noreferrer">http://commons.apache.org/proper/commons-jexl/</a>

Add the following lines to your maven <code>pom.xml</code>

<pre><code>&lt;dependency&gt;
 &lt;groupId&gt;org.apache.commons&lt;/groupId&gt;
 &lt;artifactId&gt;commons-jexl3&lt;/artifactId&gt;
 &lt;version&gt;3.1&lt;/version&gt;
&lt;/dependency&gt;
</code></pre>

Haven't tested the code below, but you can give it a go.

<pre><code>import org.apache.commons.jexl3.*;

JexlEngine jexl = new JexlBuilder().create();
String expression = "(a|b)^c";
JexlExpression jExpression = jexl.createExpression(expression);

// JexlContext stores the values for variables used in an JexlExpression
JexlContext context = new MapContext();
context.set("a", true);
context.set("b", true);
context.set("c", true);

// evaluate expression.
Long result = (Long) jExpression.evaluate(context);
System.out.println(result); // 0 for false
</code></pre>

Of course, the performance will be worse than executing the code directly because the expression have to parsed into an abstract syntax tree (AST) before it can be evaluated.

i want convert String to boolean, but Output is always false.

<pre><code>a=true;
b=true;
c=true;
String zOrginal="(a^b)|c";
boolean z= Boolean.parseBoolean(zOrginal);
out.println(z);
</code></pre>

Output is always false,

how to convert String to boolean in java?

Java

我希望将字符串转换为布尔值，但输出始终为false。a=true;b=true;c=true;String zOrginal="(a^b)|c";boolean z= Boolean.parseBoolean(zOrginal);out.println(z);输出总是假的，

问如何在java中将字符串转换为布尔值？
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