blocks|key|664615|text|假设您只想添加和乘x，只需执行以下操作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|664616|public+int+calculate(int+x,+String+str)+{
++++//+while(true)+is+gonna+get+you+into+some+trouble
++++if(+str.equals("ADD"))+{
++++++++return+x+%2B+x;
++++}
++++else+if(+str.equals("MUL"))+{
++++++++return+x+*+x;
++++}
++++else
++++++++return+x;+//+not+sure+what+you+want+to+do+in+this+case
}|code-block|syntax|javascript|664617|entityMap^0|9|1|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Assuming you are trying to just add and multiply <code>x</code>, just do the following:

<pre><code>public int calculate(int x, String str) {
 // while(true) is gonna get you into some trouble
 if( str.equals("ADD")) {
 return x + x;
 }
 else if( str.equals("MUL")) {
 return x * x;
 }
 else
 return x; // not sure what you want to do in this case
}
</code></pre>

blocks|key|868486|text|public+class+Calculator+{
++++public+static+enum+Operation+{ADD,+MUL,+SUB,+DIV};
++++private+int+x;+//+store+value+from+previous+operations

++++public+void+calculate(int+x,+Operation+operation)+{
++++++++switch(operation)+{
++++++++case+ADD:
++++++++++++this.x+%2B=+x;
++++++++++++break;
++++++++case+MUL:
++++++++++++this.x+*=+x;
++++++++++++break;
++++++++case+SUB:
++++++++++++this.x+-=+x;
++++++++++++break;
++++++++case+DIV:
++++++++++++this.x+/=+x;
++++++++++++break;
++++++++}
++++}

++++public+int+getResult()+{
++++++++return+this.x;
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|868487|要在代码的其他地方使用它：|unstyled|868488|public+static+void+main(String[]+args)+{
++++Calculator+c+=+new+Calculator();
++++c.calculate(4,+Calculator.Operation.ADD);
++++//+Other+operations
++++c.getResult();+//+get+final+result
}|868489|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>public class Calculator {
 public static enum Operation {ADD, MUL, SUB, DIV};
 private int x; // store value from previous operations

 public void calculate(int x, Operation operation) {
 switch(operation) {
 case ADD:
 this.x += x;
 break;
 case MUL:
 this.x *= x;
 break;
 case SUB:
 this.x -= x;
 break;
 case DIV:
 this.x /= x;
 break;
 }
 }

 public int getResult() {
 return this.x;
 }
}
</code></pre>

To use it elsewhere in your code:

<pre><code>public static void main(String[] args) {
 Calculator c = new Calculator();
 c.calculate(4, Calculator.Operation.ADD);
 // Other operations
 c.getResult(); // get final result
}
</code></pre>

blocks|key|1348109|text|您需要的不是运行时元编程，而是一流的函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1348110|下面表示第一类函数，分别为1和2。|1348111|abstract+class+UnaryFunction<A,+B>+{
++public+abstract+B+apply(A+a);
}

abstract+class+BinaryFunction<A,+B,+C>+{
++public+abstract+C+apply(A+a,+B+b);
}|code-block|syntax|javascript|1348112|为了简单起见，让我们使用上述类的专门版本。|1348113|abstract+class+UnaryOperation+{
++public+abstract+int+apply(int+a);
}

abstract+class+BinaryOperation+{
++public+abstract+int+apply(int+a,+int+b);
}|1348114|现在构造一个所需算术操作的字典。|1348115|Map<String,+BinaryOperation>+ops+=+new+HashMap<String,+BinaryOperation>();
ops.put("ADD",+new+BinaryOperation()+{
++public+int+apply(int+a,+int+b)+{
++++return+a+%2B+b;
++}
});
ops.put("MUL",+new+BinaryOperation()+{
++public+int+apply(int+a,+int+b)+{
++++return+a+*+b;
++}
});
//+etc.|1348116|添加对一个参数部分应用BinaryOperation的方法。|offset|length|style|CODE|1348117|abstract+class+BinaryOperation+{
++public+abstract+int+apply(int+a,+int+b);

++public+UnaryOperation+partial(final+int+a)+{
++++return+new+UnaryOperation()+{
++++++public+int+apply(int+b)+{
++++++++return+BinaryOperation.this.apply(a,+b);
++++++}
++++};
++}
}|1348118|现在我们可以编写您的calculate方法。|1348119|public+UnaryOperation+calculate(int+x,+String+opString)+{
++BinaryOperation+op+=+ops.get(opString);
++if(op+==+null)
++++throw+new+RuntimeException("Operation+not+found.");
++else
++++return+op.partial(x);
}|1348120|使用：|1348121|UnaryOperation+f+=+calculate(3,+"ADD");
f.apply(5);+//+returns+8

UnaryOperation+g+=+calculate(9,+"MUL");
f.apply(11);+//+returns+99|1348122|上述解决方案中使用的抽象，即第一类函数接口和部分应用程序，都可以在这库中使用。|1348123|entityMap|0|LINK|mutability|MUTABLE|url|http://functionaljava.org/^0|0|0|0|0|0|0|0|B|F|0|0|A|9|0|0|0|0|X|1|0|0^^$0|@$1|2|3|4|5|6|7|1G|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1H|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1I|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1J|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1K|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|1L|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1M|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|1N|8|@$S|1O|T|1P|U|V]]|9|@]|A|$]]|$1|W|3|X|5|F|7|1Q|8|@]|9|@]|A|$G|H]]|$1|Y|3|Z|5|6|7|1R|8|@$S|1S|T|1T|U|V]]|9|@]|A|$]]|$1|10|3|11|5|F|7|1U|8|@]|9|@]|A|$G|H]]|$1|12|3|13|5|6|7|1V|8|@]|9|@]|A|$]]|$1|14|3|15|5|F|7|1W|8|@]|9|@]|A|$G|H]]|$1|16|3|17|5|6|7|1X|8|@]|9|@$S|1Y|T|1Z|1|20]]|A|$]]|$1|18|3|-4|5|6|7|21|8|@]|9|@]|A|$]]]|19|$1A|$5|1B|1C|1D|A|$1E|1F]]]]

What you need is not runtime metaprogramming, but first class functions. 

The following represent first class functions, with arity 1 and 2 respectively.

<pre><code>abstract class UnaryFunction&lt;A, B&gt; {
 public abstract B apply(A a);
}

abstract class BinaryFunction&lt;A, B, C&gt; {
 public abstract C apply(A a, B b);
}
</code></pre>

For the sake of simplicity, let's use specialized versions of above classes.

<pre><code>abstract class UnaryOperation {
 public abstract int apply(int a);
}

abstract class BinaryOperation {
 public abstract int apply(int a, int b);
}
</code></pre>

Now construct a dictionary of the required arithmetic operations.

<pre><code>Map&lt;String, BinaryOperation&gt; ops = new HashMap&lt;String, BinaryOperation&gt;();
ops.put("ADD", new BinaryOperation() {
 public int apply(int a, int b) {
 return a + b;
 }
});
ops.put("MUL", new BinaryOperation() {
 public int apply(int a, int b) {
 return a * b;
 }
});
// etc.
</code></pre>

Add a method that partially applies <code>BinaryOperation</code> on one parameter.

<pre><code>abstract class BinaryOperation {
 public abstract int apply(int a, int b);

 public UnaryOperation partial(final int a) {
 return new UnaryOperation() {
 public int apply(int b) {
 return BinaryOperation.this.apply(a, b);
 }
 };
 }
}
</code></pre>

Now we can write your <code>calculate</code> method.

<pre><code>public UnaryOperation calculate(int x, String opString) {
 BinaryOperation op = ops.get(opString);
 if(op == null)
 throw new RuntimeException("Operation not found.");
 else
 return op.partial(x);
}
</code></pre>

Use:

<pre><code>UnaryOperation f = calculate(3, "ADD");
f.apply(5); // returns 8

UnaryOperation g = calculate(9, "MUL");
f.apply(11); // returns 99
</code></pre>

The abstractions used in the above solution, namely first class function interfaces and partial application, are both available in <a href="http://functionaljava.org/" rel="nofollow">this</a> library.

How I can get arithmetical operators at run-time in Java? Suppose if I have values 

<ul>
<li><code>ADD</code> it should add the number </li>
<li><code>MUL</code> then it should multiply the number</li>
</ul>

For Example

<pre><code> public calculate(int x, String str){
 while(str.equals("some value")){
 If( str.equals("ADD"))
 // it should return me something like x+
 if( str.equals("MUL"))
 it return me something like x*
 }
 if( str.equals("FINAL"))
 it should return me x+x*x

 }
</code></pre>

How to get arithmetical operators at runtime?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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如何在Java运行时获得算术运算符？假设我有价值ADD它应该加数字MUL，那么它应该乘以这个数例如  public calculate(int x, String str){   while(str.equals("some value")){     If( str.equals("ADD"))        // ...

问如何在运行时获得算术运算符？
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问如何在运行时获得算术运算符？
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