Develop Reference

Tuple Java like tuple in OPL

I have coded and run my model in OPL, and I am trying to run code it in JAVA and run it again. As part of my Code (in OPL), I have defined a Tuple as follows:
int Y = asSet(1..7);
int k = asSet(1..42);
int G = asSet(1..2);
tuple SL {
int i;
int j;
float l;
}
{SL} SLs with i,j in Y=...; /* e.g. {<1,2,502>, <2,5,309>, <5,7,401>, <2,3,350>} */
Then, I have defined other arrays of:
int u[SLs][G]=...; /* e.g. u[<1,2,502>][1] = 50; u[<1,2,502>][2] = 83; u[<2,5,309>][1] = 75;*/
Now that I wanted to code it in Java, I have done it as follows, but I am not sure if I am right. I would appreciate if you could share your ideas.
import java.io.*;
import java.util.*;
public class Model {
public static int Y = 7;
public static int K = 42;
public static int G = 3;
public static int R = 2;
public class SL {
public int i; /* how say i is in Y*/
public int j; /* how say j is in Y*/
public int l;
List<SL> sl = new ArrayList<SL>();
Object[] SL1 = Sl.toArray();
int [][] u = new int [sL.length][G];
}
public static void Solve() {
/* How to instantiate SL1 and u[<i,j,l> in SL1][g in G] here and printout SL1:*/
}
}
and another class to run the solve() method:
public class SolverMethod {
public static void main(String[] args) {
Model.Solve();
}
}
I would appreciate if you help me out to fix and run the code.
Regards,
Bornay

You may make Map so that with tuple or object of SL you can generate unique number which can be used as a index in u var. say,
Map<SL,Integer> m;
int key=m.get(sl);
u[key][g]
and to instatiate SL1 you need to make object of SL since SL1 is not static.
SL sl=new SL();
sl.SL1 or sl.u
First create object of SL and point it's variables or methods.
Here is my implemented code below. I have made some changes.
import java.io.*;
import java.util.*;
public class Model {
public static int Y = 7;
public static int K = 42;
public static int G = 3;
public static int R = 2;
static Map<SL,Integer> m=new HashMap<>();
static List<SL> sL = new ArrayList<SL>();
static int[][] u;
static int index=0;
static public class SL {
public int i;
/* how say i is in Y*/
public int j;
/* how say j is in Y*/
public int l;
}
public static void Solve() {
/* How to instantiate SL1 and u[<i,j,l> in SL1][g in G] here and printout SL1:*/
for(int i=0;i<5;i++){
SL sl=new SL();
sl.i=i;sl.j=i+1;sl.l=i+2;
sL.add(sl);
m.put(sl, index++);
}
u=new int[m.size()][G];
for(SL s:sL){
for(int i=0;i<G;i++){
u[m.get(s)][i]=i+10;
}
}
for(SL s:sL){
for(int i=0;i<G;i++){
System.out.println(u[m.get(s)][i]);
}
}
}
public static void main(String[] arg){
Model.Solve();
}
}
Here I have made sL,m and u static because we need only single instance of it.

How to pass the correct value when calling a method?

I'm doing an assignment in which I have created an Appliance class that has a timePasses()method within it. This method re-directs some values that need to be stored within another method that is inside of another class. Here is where I am up to on this:
Appliance
public class ElectricCooker extends Cooker {
public int isOn = -1;
public int isOff = 0;
public int incrementTime;
public int varPass = -1;
#Override
public int currentState() {
if (varPass == 0) {
return isOff;
} else {
return isOn;
}
}
#Override
public void useTime(int defaultTime) {
defaultTime = 15;
incrementTime = 4;
}
#Override
public void timePasses() {
if (varPass == isOff) {
varPass = 0;
} else {
ElectricMeter.getInstance().incrementConsumed(electricityUse);
GasMeter.getInstance().incrementConsumed(gasUse);
WaterMeter.getInstance().incrementConsumed(waterUse);
}
}
ElectricCooker(int electricityUse, int gasUse, int waterUse, int timeOn) {
super(electricityUse, gasUse, waterUse, timeOn);
this.electricityUse = 5 * incrementTime;
this.gasUse = 0 * incrementTime;
this.waterUse = 0 * incrementTime;
this.timeOn = 15 * incrementTime;
}
}
Meter
public class ElectricMeter {
ElectricMeter() {
}
private static ElectricMeter instance = new ElectricMeter();
public static ElectricMeter getInstance() {
return instance;
}
public void incrementConsumed(int value) {
System.out.println(value);
}
public int incrementGenerated() {
}
public boolean canGenerate() {
}
public String getConsumed() {
}
public String getGenerated() {
}
}
Main method
public class MainCoursework {
public static void main(String[] args) {
ElectricMeter a = new ElectricMeter();
a.incrementConsumed(//what goes here?);
}
}
So the value from timePasses()has been redirected into an ElectricMeter instance but now I need to return that value to the increentConsumed() method in the meter class and I'm stuck on how to do this. Since the value of electricityConsumed is 20, the output should be 20. But instead I have to pass a parameter into a.incrementConsumed(//pass parameter here) and what ever is passed gets printed out onto the screen instead of the 20 from electrictyUse. Any help on how to do this is appreciated, thanks.

Actually, the incrementConsumed method is indeed implemented as you described:
public void incrementConsumed(int value)
{
System.out.println(value);
}
A method called incrementXXX shouldn't really output anything, should it? It should increment a variable/field:
private int electricityUsed = 0;
public void incrementConsumed(int value)
{
electricityUsed += value;
}
You should declare another method that returns electricityUsed:
public int getElectricityUsed() {
return electricityUsed;
}
Now let's fix your main method.
In your main method, you didn't even create anything that consumes electricity! How can the electric meter incrementConsumed? So remove everything from the main method and create a cooker:
// your constructor looks weird. So I passed in some random arguments..
ElectricCooker cooker = new ElectricCooker(20, 0, 0, 60);
Now call timePasses to simulate that some time passed:
cooker.timePasses();
And print the electricity used:
System.out.println(ElectricMeter.getInstance().getElectricityUsed());

you need to create an instance variable in ElectricMeter and update that value on say incrementConsumed. When you want to print that use accessor of this variable.
public class Electric {
public static void main(String[] args) {
ElectricCooker cooker = new ElectricCooker(1,2,3,4);
//opertion on cooker
//ignoring best way for singleton creation
int electricityUse = ElectricMeter.getInstance().getElectricityUse();
System.out.println(electricityUse);
}
}
class ElectricCooker // extends Cooker
{
public int isOn = -1;
public int isOff = 0;
public int incrementTime;
public int varPass = -1;
public int electricityUse = -1;
public int currentState() {
if (varPass == 0)
return isOff;
else {
return isOn;
}
}
public void useTime(int defaultTime) {
defaultTime = 15;
incrementTime = 4;
}
public void timePasses() {
if (varPass == isOff)
varPass = 0;
else {
ElectricMeter.getInstance().incrementConsumed(electricityUse);
}
}
ElectricCooker(int electricityUse, int gasUse, int waterUse, int timeOn) {
this.electricityUse = 5 * incrementTime;
}
}
class ElectricMeter {
public int electricityUse = -1;
private static ElectricMeter instance = new ElectricMeter();
public static ElectricMeter getInstance() {
return instance;
}
public void incrementConsumed(int value) {
this.electricityUse = value;
}
public int getElectricityUse() {
return electricityUse;
}
}

In ElectricMeter, some operations don't perform what they should.
ElectricMeter.getInstance().incrementConsumed(electricityUse);
should increment something but it writes only in the output:
public void incrementConsumed(int value){
System.out.println(value);
}
You should write it rather :
public void incrementConsumed(int value){
consumed+=value;
}
and add a private int consumed field in ElectricMeter class to store the actual consumed.
And your getConsumed() which has a empty implementation :
public String getConsumed(){
}
should simply return the consumed field and you should return a int value and not a String.
public int getConsumed() {
return consumed;
}
In this way, you can do :
public static void main(String[] args){
ElectricMeter.getInstance().incrementConsumed(20);
int consumed = ElectricMeter.getInstance().getConsumed();
}

How can I invoke a method and print its result?

How can I invoke a method and print its result?
public class Test {
public static int main (String args[]){
System.out.println(total);
}
public int numbers (int a, int b){
int total;
total = a + b;
return = total;
}
}

Try this instead:
public class Test {
public static void main (String args[]){
System.out.println(numbers(1, 2));
}
public static int numbers(int a, int b){
int total;
total = a + b;
return total;
}
}
Variables are scoped to the method or class in which they are defined, therefore the 'total' variable is accessible only in the 'numbers' method

public class Test {
public static void main (String args[]){
System.out.println(numbers(anumber,bnumber));
}
public static int numbers (int a, int b){
int total;
total = a + b;
return total;
}

Passing dynamic primitive type (int) to a method

In Java, the output of s is 0. I do not understand why and would it be possible to somehow get the correct value of s (1000 here)?
public static void main(String args) {
int s = 0;
List<Integer> list = getList(s);
System.out.println("s = " + s);
}
public static List<Integer> getList(int s) {
List<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < 1000; i++) {
list.add(i); s++;
}
}
In C# there were out descriptors to indicate that the variable is going to change if I'm not mistaken..
I'm not going to get the list.size() in general!

In Java, all method arguments are passed by value, i.e. copy. So, changes to the copy are not visible to the caller.
To address your second question, you can just use list.size() on the caller side.

I see two ways
1) Make 's' as static variable and move it to class level
2) Create class with getter/setter for list and int and return the object for getList call
public static MyWrapperObj getList(int s) {
......
return wrapperObj
}
class MyWrapperObj
{
private List<Integer>;
private countS;
....
//getter/setters.
}

Java doesn't allow for passing parameters by reference - but you could wrap it in an object like this:
class IntHolder {
private int s;
IntHolder(int s){
this.s = s;
}
public void setS(int s){
this.s = s;
}
public int getS(){
return s;
}
public void increment(){
s++;
}
}
class Test{
public static void main(String[] args) {
IntHolder s = new IntHolder(0);
List<Integer> list = getList(s);
System.out.println("s = " + s.getS());
}
public static List<Integer> getList(IntHolder s) {
List<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < 1000; i++) {
list.add(i); s.increment();
}
return list;
}
}

In java, arguments passed to methods are passed by value.. you will need to make s a global or instance variable in order to modify it in other methods. This is just the way java works. e.g.
public class Test{
private int s;
public Test(){
s=0;
increment();
//print now will be 1000.
}
private void increment(){
s = 1000;
}
}

Java 'this' keyword

I'm just beginning in programming and I'd like to make exercise from a book, but I can't. That's my problem:
public class increment {
int increment() {
return this + 1; // aka this++
}
public static void main(String[] args) {
int a = 0;
System.out.println(a.increment());
}
}
As you for sure guessed already, that it doesn't works, I want to ask you how to get outputed integer a incremented by one, but using keyword 'this'.
Regards and sorry for stupid questions.

It is strange to name a class like a method.
I guess you wanted this:
public class Counter {
int val;
public Counter (int start) {
val = start;
}
public void increment() {
val ++;
}
public String toString () {
return Integer.toString (val);
}
public static void main(String[] args) {
Counter counter = new Counter (0);
counter.increment ();
System.out.println(counter.toString ());
}
}

this is an object (the current object). You cannot "increment" it.
A way to do it is:
public class Increment {
int a = 0;
int increment() {
return a + 1;
// or: return this.a + 1;
// or: a++; return a; if you want a to be incremented from now on
}
public static void main(String[] args) {
Increment inc = new Increment();
System.out.println(inc.increment());
}
}

The this keyword in Java refers to the current scope's object instance. I don't think it's what you're looking for in this case.
In your example, a isn't an object of the class increment, it is a primitive int. In order to use the .increment() function you defined, it would have to be an object of type increment.
One option that may be what you're looking for would be the following.
public class Increment { //Java likes capitalized class names
private int myInt;
public Increment(int a) { //constructor
myInt = a;
}
public int increment() {
return ++myInt;
}
public static void main(String[] args) {
Increment a = new Increment(0);
System.out.println(a.increment());
}
}
In this example, we make a new class of type increment, which internally contains an integer. Its increment method increments that internal integer, and then returns the number.

you are using operator + for your current object (this). Operator overloading is not supported in java.

Something like this will work:
class MyInteger {
private int internal;
public MyInteger( int value ){
this.internal = value;
}
public int incerment(){
return ++this.internal;
}
}
public class Increment {
public static void main(String[] args) {
MyInteger a = new MyInteger(0);
System.out.println(a.increment());
}
}
You see, you can only implement methods for your own classes, not for existing classes, or for primitives like int.

i don't think you can use this to return the value, except if you're making a new class like this:
class Increment1
{
private int a;
public int increment2(int a)
{
this.a=a;
return this.a + 1;
}
}
public class Increment
{
static Increment1 b = new Increment1();
public static void main(String[] args)
{
int a = 0;
System.out.println(b.increment2(a));
}
}

You cannot increment a class like this.
You have to use a member variable that you can increment.
public class Test {
private int var;
public Test(int i) {
this.var = i;
}
int increment() {
this.var++;
}
}
public static void main(String[] args) {
Test t = new Test(0);
System.out.println(t.increment());
}

This refers to the current instance of the class, not a particular member.
You want to increment a property (I'm guessing of type long or int), and not the instance of your increment class (should be Increment, by the way).
Something like this would work:
public class increment {
private int innerValue = 0;
int increment() {
innerValue+=1
return innerValue; // aka this++
}
public static void main(String[] args) {
increment a = new increment()
System.out.println(a.increment());
}
}