code is as follows:

package referenceCoutingGC;

/**
 * 
 * testGC()ogjAogjBGC
 *
 */
public class referenceCoutingGC {
    
    public Object instance = null;
    
    private static final int _1MB = 1024*1024;
    
    private byte[] bigSize = new byte[2*_1MB];
    
    public static void testGC(){
        referenceCoutingGC objA = new referenceCoutingGC();
        referenceCoutingGC objB = new referenceCoutingGC();
        objA.instance = objB;
        objB.instance = objA;
        
        objA = null;
        objB = null;
        
        //GCobjAobjB?
        System.gc();
        System.out.println("");
    }
    public static void main(String[] args){
        
        testGC();
        
    }
}

there are output results in the book. The words 4603k-> 210k are also specifically stated.

mine is jdk 1.8