SWIG/Examples/java/reference/main.java

// file: main.java

// This file illustrates the manipulation of C++ references in Java.

import example;

public class main {
  static {
    try {
        System.loadLibrary("example");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Cannot load the example native code.\nMake sure your LD_LIBRARY_PATH contains \'.\'\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[]) 
  {
    System.out.println( "Creating some objects:" );
    Vector a = new Vector(3,4,5);
    Vector b = new Vector(10,11,12);
    
    System.out.println( "    Created " + a.print() );
    System.out.println( "    Created " + b.print() );
    
    // ----- Call an overloaded operator -----
    
    // This calls the wrapper we placed around
    //
    //      operator+(const Vector &a, const Vector &) 
    //
    // It returns a new allocated object.
    
    System.out.println( "Adding a+b" );
    Vector c = new Vector (example.addv(a.getCPtr(),b.getCPtr()), false);
    System.out.println( "    a+b = " + c.print() );
    
    // Note: Unless we free the result, a memory leak will occur
    // This is because we used 'false' for cMemoryOwn in the constructor of c.
    // If we had used 'true', the memory management is best left to the garbage collector.
    // You can still call _delete(). It will free the c++ memory immediately, but not the 
    // Java memory! You then must be careful not to call any member functions as it will 
    // use a NULL c pointer on the underlying c++ object.
    c._delete();
    
    // ----- Create a vector array -----
    
    // Note: Using the high-level interface here
    System.out.println( "Creating an array of vectors" );
    VectorArray va = new VectorArray(10);
    System.out.println( "    va = " + va.toString() );
    
    // ----- Set some values in the array -----
    
    // These operators copy the value of Vector a and Vector b to the vector array
    va.set(0,a);
    va.set(1,b);
    
    // This will work, but it will cause a memory leak!
    // This is the low level way of using Java with SWIG and isn't very readable!
    
    example.VectorArray_set(va.getCPtr(),2,example.addv(a.getCPtr(),b.getCPtr()));
    
    // The non-leaky way to do it. This is the high level way of using Java with SWIG.
    // This relies on the garbage collector for freeing memory
    // An even better way would have been possible if addv was a static function in the 
    // c++ class. The code would then instead be:
    // c = Vector.addv(a,b); 
    
    c = new Vector(example.addv(a.getCPtr(),b.getCPtr()), true);
    va.set(3,c);
    
    // Get some values from the array
    
    System.out.println( "Getting some array values" );
    for (int i=0; i<5; i++)
        System.out.println( "    va(" + i + ") = " + va.get(i).print() );
    
    // Watch under resource meter to check on this
    System.out.println( "Making sure we don't leak memory." );
    for (int i=0; i<1000000; i++)
        c = va.get(i%10);
    
    // ----- Clean up -----
    // This could be omitted. The garbage collector would then clean up for us.
    System.out.println( "Cleaning up" );
    va._delete();
    a._delete();
    b._delete();
  }
}