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  31 
  32 // Usage: jjs javacastcounter.js -- <.java files>
  33 
  34 // This example demonstrates Nashorn Java.extend API
  35 // to subclass a Java class from script.
  36 
  37 // This example uses Javac Compiler and Tree API
  38 // to list type casts used in java source files.
  39 
  40 if (arguments.length == 0) {
  41     print("Usage: jjs javacastcounter.js -- <.java files>");
  42     exit(1);
  43 }
  44 
  45 // Java types used
  46 var ToolProvider = Java.type("javax.tools.ToolProvider");
  47 var TreeScanner = Java.type("com.sun.source.util.TreeScanner");
  48 var Trees = Java.type("com.sun.source.util.Trees");
  49 var StringArray = Java.type("java.lang.String[]");
  50 
  51 // get the system compiler tool
  52 var compiler = ToolProvider.systemJavaCompiler;
  53 
  54 // get standard file manager
  55 var fileMgr = compiler.getStandardFileManager(null, null, null);
  56 
  57 // make a list of compilation unit from command line argument file names
  58 // Using Java.to convert script array (arguments) to a Java String[]
  59 var compUnits = fileMgr.getJavaFileObjects(Java.to(arguments, StringArray));
  60 
  61 // create a new compilation task
  62 var task = compiler.getTask(null, fileMgr, null, null, null, compUnits);
  63 
  64 // SourcePositions object to get positions of AST nodes
  65 var sourcePositions = Trees.instance(task).sourcePositions;
  66 
  67 // Subclass TreeScanner class
  68 var CastCounter = Java.extend(TreeScanner);
  69 
  70 var counter = new CastCounter() {
  71     // current CompilationUnitTree
  72     compUnit: null,
  73     // current LineMap (pos -> line, column)
  74     lineMap: null,
  75     // current compilation unit's file name
  76     fileName: null,
  77 
  78     // overrides of TreeScanner methods
  79 
  80     visitCompilationUnit: function(node, p) {
  81         // capture info about current Compilation unit
  82         this.compUnit = node;
  83         this.lineMap = node.lineMap;
  84         this.fileName = node.sourceFile.name;
  85 
  86         // Using Java.super API to call super class method here
  87         return Java.super(counter).visitCompilationUnit(node, p);
  88     },
  89 
  90     visitTypeCast: function(node, p) {
  91         // print information on this type cast node
  92         var pos = sourcePositions.getStartPosition(this.compUnit, node);
  93         var line = this.lineMap.getLineNumber(pos);
  94         var col = this.lineMap.getColumnNumber(pos);
  95         print(node + " @ " + this.fileName + ":" + line + ":" + col);
  96 
  97         // count one more type cast
  98         return 1;
  99     },
 100 
 101     reduce: function(r1, r2) {
 102         return (r1 == null ? 0 : r1) + (r2 == null ? 0 : r2);
 103     }
 104 };
 105 
 106 // print total number of type cast nodes seen
 107 print("Total casts:", counter.scan(task.parse(), null));