samples/javacastcounter.js

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// Usage: jjs javacastcounter.js -- <.java files>

// This example demonstrates Nashorn Java.extend API
// to subclass a Java class from script.

// This example uses Javac Compiler and Tree API
// to list type casts used in java source files.

if (arguments.length == 0) {
    print("Usage: jjs javacastcounter.js -- <.java files>");
    exit(1);
}

// Java types used
var ToolProvider = Java.type("javax.tools.ToolProvider");
var TreeScanner = Java.type("com.sun.source.util.TreeScanner");
var Trees = Java.type("com.sun.source.util.Trees");
var StringArray = Java.type("java.lang.String[]");

// get the system compiler tool
var compiler = ToolProvider.systemJavaCompiler;

// get standard file manager
var fileMgr = compiler.getStandardFileManager(null, null, null);

// make a list of compilation unit from command line argument file names
// Using Java.to convert script array (arguments) to a Java String[]
var compUnits = fileMgr.getJavaFileObjects(Java.to(arguments, StringArray));

// create a new compilation task
var task = compiler.getTask(null, fileMgr, null, null, null, compUnits);

// SourcePositions object to get positions of AST nodes
var sourcePositions = Trees.instance(task).sourcePositions;

// Subclass TreeScanner class
var CastCounter = Java.extend(TreeScanner);

var counter = new CastCounter() {
    // current CompilationUnitTree
    compUnit: null,
    // current LineMap (pos -> line, column)
    lineMap: null,
    // current compilation unit's file name
    fileName: null,

    // overrides of TreeScanner methods

    visitCompilationUnit: function(node, p) {
        // capture info about current Compilation unit
        this.compUnit = node;
        this.lineMap = node.lineMap;
        this.fileName = node.sourceFile.name;

        // Using Java.super API to call super class method here
        return Java.super(counter).visitCompilationUnit(node, p);
    },

    visitTypeCast: function(node, p) {
        // print information on this type cast node
        var pos = sourcePositions.getStartPosition(this.compUnit, node);
        var line = this.lineMap.getLineNumber(pos);
        var col = this.lineMap.getColumnNumber(pos);
        print(node + " @ " + this.fileName + ":" + line + ":" + col);

        // count one more type cast
        return 1;
    },

    reduce: function(r1, r2) {
        return (r1 == null ? 0 : r1) + (r2 == null ? 0 : r2);
    }
};

// print total number of type cast nodes seen
print("Total casts:", counter.scan(task.parse(), null));