Week # 4 – Exercises / Solutions
Exercise #1: Consider the following class definition:
public class Complex {
private double re;
private double im;
private static int instanceCount = 0;
public Complex(double real, double imag)
re = real;
im = imag;
}
}
Identify the Local Variables in the Complex constructor?
Identify the Instance Variables in the above Class definition?
Identify the Class Variables in the above Class definition?
For all the local variables identified in the above Complex constructor, indicate
their slot numbers. Also, discuss if a local variable needs more than one slot and
why?
Local Variables
this reference (as non-static)
real and imag (parameters)
Instance Variables
re and im
Class Variables
instanceCount as declared static
Slot Numbers
this reference – Slot # 0
real – Slot # 1 (needs to two slots, as its double; actually takes slots 1 & 2)
imag – Slot # 3 (needs to two slots, as its double; actually takes slots 3 & 4)
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Exercise #2: Show how the following values would be stored in a byte-addressable
machines with 32-bit words, using little endian and then big endian format. Assume that
each value starts at address 1016. Draw a diagram of memory for each, placing the
appropriate values in the correct (and labeled) memory locations.
0x456789A1
0x0000058A
0x14148888
For 0x456789A1
Memory Address 1016 1017 1018 1019
Little Endian A1 89 67 45
Big Endian 45 67 89 A1
For 0x0000058A
Memory Address 1016 1017 1018 1019
Little Endian 8A 05 00 00
Big Endian 00 00 05 8A
For 0x14148888
Memory Address 1016 1017 1018 1019
Little Endian 88 88 14 14
Big Endian 14 14 88 88
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Exercise #3: Now, introduce the following method definitions to the Complex class
seen above, and then use javap to disassemble the compiled bytecode (.class) file.
public Complex plus(Complex b){
Complex a = this;
double real = a.re + b.re;
double imag = a.im + b.im;
return new Complex(real, imag);
}
public static void main(String[] args){
Complex a = new Complex(5.0, 6.0);
Complex b = new Complex(-3.0, 4.0);
System.out.println(”a + b = ” + a.plus(b));
}
How many local variables are created in the stack frame of plus method? List all
of them and mention their slot numbers as well as data types.
A total of five local variables are created on the stack frame of plus method.
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Which instructions in the bytecode for plus method correspond to the Java
source code?
The plus method from above class is compiled into bytecode as follows:
The bytecode to Java source code mapping is given below:
What is the purpose of invokespecial instruction in the bytecode of plus method?
The invokespecial instruction at the end of bytecode is
required to create a new object of Complex type, which is
then returned to the calling method.
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