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langtools/test/tools/javac/api/evalexpr/CompileFromString.java

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+/*
+ * Copyright 2005-2006 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+package evalexpr;
+
+import java.lang.reflect.Method;
+import java.util.*;
+import javax.swing.JOptionPane;
+import javax.tools.*;
+import static javax.tools.StandardLocation.CLASS_OUTPUT;
+
+/**
+ * JSR 199 Demo application: compile from a String.
+ *
+ * <p><b>This is NOT part of any API supported by Sun Microsystems.
+ * If you write code that depends on this, you do so at your own
+ * risk.  This code and its internal interfaces are subject to change
+ * or deletion without notice.</b></p>
+ *
+ * @author Peter von der Ah&eacute;
+ */
+public class CompileFromString {
+
+    /**
+     * The name of the class used to evaluate expressions.
+     */
+    private final static String CLASS_NAME = "EvalExpression";
+
+    /**
+     * Object used to signal errors from evalExpression.
+     */
+    public final static Object ERROR = new Object() {
+        public String toString() { return "error"; }
+    };
+
+    /**
+     * Compile and evaluate the specified expression using the
+     * given compiler.
+     * @param compiler a JSR 199 compiler tool used to compile the given expression
+     * @param expression a Java Programming Language expression
+     * @return the value of the expression; ERROR if any errors occured during compilation
+     * @throws java.lang.Exception exceptions are ignored for brevity
+     */
+    public static Object evalExpression(JavaCompiler compiler,
+                                        DiagnosticListener<JavaFileObject> listener,
+                                        List<String> flags,
+                                        String expression)
+        throws Exception
+    {
+        // Use a customized file manager
+        MemoryFileManager mfm =
+            new MemoryFileManager(compiler.getStandardFileManager(listener, null, null));
+
+        // Create a file object from a string
+        JavaFileObject fileObject = mfm.makeSource(CLASS_NAME,
+            "public class " + CLASS_NAME + " {\n" +
+            "    public static Object eval() throws Throwable {\n" +
+            "        return " + expression + ";\n" +
+            "    }\n}\n");
+
+        JavaCompiler.CompilationTask task =
+            compiler.getTask(null, mfm, listener, flags, null, Arrays.asList(fileObject));
+        if (task.call()) {
+            // Obtain a class loader for the compiled classes
+            ClassLoader cl = mfm.getClassLoader(CLASS_OUTPUT);
+            // Load the compiled class
+            Class compiledClass = cl.loadClass(CLASS_NAME);
+            // Find the eval method
+            Method eval = compiledClass.getMethod("eval");
+            // Invoke it
+            return eval.invoke(null);
+        } else {
+            // Report that an error occured
+            return ERROR;
+        }
+    }
+
+    /**
+     * Main entry point for program; ask user for expressions,
+     * compile, evaluate, and print them.
+     *
+     * @param args ignored
+     * @throws java.lang.Exception exceptions are ignored for brevity
+     */
+    public static void main(String... args) throws Exception {
+        // Get a compiler tool
+        final JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
+        final List<String> compilerFlags = new ArrayList();
+        compilerFlags.add("-Xlint:all"); // report all warnings
+        compilerFlags.add("-g:none"); // don't generate debug info
+        String expression = "System.getProperty(\"java.vendor\")";
+        while (true) {
+            expression = JOptionPane.showInputDialog("Please enter a Java expression",
+                                                     expression);
+            if (expression == null)
+                return; // end program on "cancel"
+            long time = System.currentTimeMillis();
+            Object result = evalExpression(compiler, null, compilerFlags, expression);
+            time = System.currentTimeMillis() - time;
+            System.out.format("Elapsed time %dms %n", time);
+            if (result == ERROR)
+                System.out.format("Error compiling \"%s\"%n", expression);
+            else
+                System.out.format("%s => %s%n", expression, result);
+        }
+    }
+}