Data commit

Task/Runtime-evaluation-In-an-environment/Java/runtime-evaluation-in-an-environment.java

@@ -0,0 +1,68 @@
+import java.io.File;
+import java.lang.reflect.Method;
+import java.net.URI;
+import java.util.Arrays;
+import javax.tools.JavaCompiler;
+import javax.tools.SimpleJavaFileObject;
+import javax.tools.ToolProvider;
+
+public class Eval {
+    private static final String CLASS_NAME = "TempPleaseDeleteMe";
+
+    private static class StringCompiler
+            extends SimpleJavaFileObject {
+        final String m_sourceCode;
+
+        private StringCompiler( final String sourceCode ) {
+            super( URI.create( "string:///" + CLASS_NAME + Kind.SOURCE.extension ), Kind.SOURCE );
+            m_sourceCode = sourceCode;
+        }
+
+        @Override
+        public CharSequence getCharContent( final boolean ignoreEncodingErrors ) {
+            return m_sourceCode;
+        }
+
+        private boolean compile() {
+            final JavaCompiler javac = ToolProvider.getSystemJavaCompiler();
+
+            return javac.getTask( null, javac.getStandardFileManager( null, null, null ),
+                null, null, null, Arrays.asList( this )
+            ).call();
+        }
+
+        private double callEval( final double x )
+                throws Exception {
+            final Class<?> clarse = Class.forName( CLASS_NAME );
+            final Method   eval   = clarse.getMethod( "eval", double.class );
+
+            return ( Double ) eval.invoke( null, x );
+        }
+    }
+
+    public static double evalWithX( final String code, final double x )
+            throws Exception {
+        final StringCompiler sc = new StringCompiler(
+            "class "
+                + CLASS_NAME
+                + "{public static double eval(double x){return ("
+                + code
+                + ");}}"
+            );
+
+        if ( ! sc.compile() ) throw new RuntimeException( "Compiler error" );
+        return sc.callEval( x );
+    }
+
+    public static void main( final String [] args )
+            throws Exception /* lazy programmer */ {
+        final String expression = args [ 0 ];
+        final double x1         = Double.parseDouble( args [ 1 ] );
+        final double x2         = Double.parseDouble( args [ 2 ] );
+
+        System.out.println(
+            evalWithX( expression, x1 )
+            - evalWithX( expression, x2 )
+        );
+    }
+}