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Wants static but can't support?

I am trying to create a random car generator that also displays info. I thought I had everything until the randomCar portion. It says that
'com.company.Main.this' cannot be referenced from a static context
under the return statements in the switch. Any thought on to where I may be going wrong?
package com.company;
public class Main {
class Car{
private String name;
private boolean engine;
private int cylinders;
private int wheels;
public Car(String name){
this.name = name;
}
public String getName(){
return name;
}
public int getCylinders() {
if(cylinders == 0){
System.out.println("Unknown amount of cylinders");
}
return cylinders;
}
public int getWheels() {
return wheels;
}
public boolean isEngine() {
return engine;
}
}
class Tacoma extends Car{
public Tacoma(String name) {
super("Tacoma");
}
public boolean isEngine(boolean engine) {
return true;
}
public int getCylinders(int cylinders) {
return 6;
}
public int getWheels(int wheels) {
return 4;
}
}
class Motorcycle extends Car{
public Motorcycle(String name) {
super("Harley Davidson");
}
public boolean isEngine(boolean engine) {
return true;
}
public int getCylinders(int cylinders) {
return 2;
}
public int getWheels(int wheels) {
return 2;
}
}
class Volvo extends Car{
public Volvo(String name) {
super("Volvo");
}
public boolean isEngine(boolean engine) {
return true;
}
public int getCylinders(int cylinders) {
return 4;
}
public int getWheels(int wheels) {
return 4;
}
}
public static void main(String[] args) {
for (int i = 1; i<6; i++){
Car car = randomCar();
System.out.println("Car # " + i + ":" + car.getName() + "\n" +
"Number of cylinders: " + car.getCylinders() + "\n" +
"Number of wheels: " + car.getWheels()+ "\n" +
"Engine is: " + car.isEngine());
}
}
private static Car randomCar() {
int randomNumber = (int) (Math.random()*5) +1;
System.out.println("Random number generated is: " + randomNumber);
switch (randomNumber){
case 1:
return new Tacoma(); // This is where I am getting an error
case 2:
return new Motorcycle(); // This is where I am getting an error
case 3:
return new Volvo(); // This is where I am getting an error
}
return null;
}
}

I would start by reading here: https://docs.oracle.com/javase/tutorial/java/javaOO/nested.html -> actually all the chapters there would be useful for you to read: https://docs.oracle.com/javase/tutorial/java/javaOO/index.html
Strictly speaking, to solve your "cannot be referenced from a static context" you can just make your classes static (Car, Tacoma, Motorcycle, Volvo) static class Car{
From my point of view you don't need nested classes, just create the classes in the same package as your Main class and you should be good to go (feel free to create more packages to better structure your classes)
Also I'm assuming your code is a work in progress because there are multiple issues with it:
methods like this don't make sense public boolean isEngine(boolean engine) {return true;} You receive a parameter that you ignore and you return a constant value: true; What I assume you want to do here is to have different types of cars each with its own predefined characteristics, but for that you should set the values for the attributes in the parent, Car. For this you either define protected setters, make the fields protected, or, best, create constructor which takes all the values
public Car(String name, boolean engine, int cylinders, int wheels) {
this.name = name;
this.engine = engine;
this.cylinders = cylinders;
this.wheels = wheels;
}
and you can have in Tacoma
public Tacoma(String name) {
super(name, true, 6, 4);
}
running your code I got the randomNumber 5 so that returned null and got a NPE, I assume work in progress
in your switch you are calling the default constructor new Tacoma() however that isn't available anymore since you defined a constructor with a parameter, use the available constructor or create the no-arg constructor.
There are other concerns regarding OOP principles so I recommend reading them again, just google "java OOP principles" and then "SOLID"... there are a lot of great resources out there, you just need time and patience and you'll get there!

When you put the Car class definition inside the class definition of Main, you made Car an inner class, so that a Car requires an outer class Main instance. In the static method there is no Main instance, and you can’t create the Car without it.
There is an immediate fix: add keyword static to the Car class:
static class Car {
which means there is no link to the enclosing object.
But there is no benefit here to making this a nested class, it would be better not to put one class definition inside another when you’re starting out.

The inner classes you've defined are instance members, meaning they belong to a specific instance of Main, and thus cannot be referenced from a static context that doesn't have a Main instance. The easiest way to resolve this would be to declare all the inner classes static.

First of all, to solve your error: 'com.company.Main.this' cannot be referenced from a static context, make all the methods static:
static class Car{//code here}
static class Volvo extends Car{//code here}
static class Tacoma extends Car{//code here}
static class Motorcycle extends Car{//code here}
Whenever you see that error, it means one static method is calling a non-static method. Therefore, just make both non-static or both static. The only exception is public static void main(String[] args); which must be static.
After solving the original errors, there is more to debug:
'Volvo(java.lang.String)' in 'com.company.Main.Volvo' cannot be applied to '()'
'Motorcycle(java.lang.String)' in 'com.company.Main.Motorcycle' cannot be applied to '()'
'Tacoma(java.lang.String)' in 'com.company.Main.Tacoma' cannot be applied to '()'
All this means is that your methods Tacoma(), Volvo(), and Motorcycle() require the parameter String name. So all you have to do is give them a name: here, it's
`new Tacoma("cool")`
new Volvo("car")
new Motorcycle("harley davidson")`
Finally, after solving the static and parameter problems, you are getting a NullPointerException, because randomCar() returns null. Your method says Car randomCar(), indicating it will return a Car, but then the return statement was return null;. Therefore, just return a Car - rtn here for our purposes:
private static Car randomCar() {
int randomNumber = (int) (Math.random()*5) +1;
System.out.println("Random number generated is: " + randomNumber);
Car rtn = null;
switch (randomNumber){
case 1:
rtn = new Tacoma("cool"); // This is where I am getting an error
case 2:
rtn = new Motorcycle("harley davidson"); // This is where I am getting an error
case 3:
rtn = new Volvo("car"); // This is where I am getting an error
}
return rtn;
}
This isn't all the debugging your code needs, but it's a start: here's what the system did so far:
Random number generated is: 3
Unknown amount of cylinders
Car # 1:Volvo
Number of cylinders: 0
Number of wheels: 0
Engine is: false
Random number generated is: 5
Hooray!
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Constructors and methods in java

I want to create the below class
associatename:String
workstatus:String
associate() :constructor
getassociatename():String
setassociatename(String):void
getworkstatus()String
tracksassociatestatus():int
setworkstatus(String):void
The trackAssociateStatus method takes the number of days as argument and sets the work status of the associate based on the number of days. The first 20 days they learn “C”, the next 20 days they learn “Java” In the Main class invoke the trackAssociateStatus method and find the work status and display the output.
output:The associate abc work status:Project phase
I tried this....But i got error
//associate class
public class associate{
private int associatename;
private String workstatus;
private int days;
void associate()
{
getassociatename();
setassociatename();
getworkstatus();
tracksassociatestatus();
setworkstatus();
}
public int getassociatename()
{
return associatename;
}
public void setassociatename(int associatename)
{
this.associatename=associatename;
}
public String getworkstatus()
{
return workstatus;
}
public void tracksassociatestatus(int days)
{
if(days<20)
setworkstatus("C");
else
setworkstatus("Java");
}
public void setworkstatus(String workstatus)
{
this.workstatus=workstatus;
}
}
//main class
associate a =new associate();
Scanner in=new Scanner(System.in);
int associateid=0;
String workstatus=null;
int days=0;
System.out.println("Enter the associateid:");
associateid=in.nextInt();
a.associateid=(associateid);
System.out.println("Enter the no of days:");
days=in.nextInt();
a.trackassociatestatus();
System.out.println("The id is "+a.getassocaiteid()+" work status "+a.getworkstatus());

Based on your (seemingly) UML spec, your class would look like the following:
public class Associate {
private String associateName;
private String workStatus;
public Associate() {
// This constructor is optional, a no-args constructor is added by the compiler to any class not explicitly naming a constructor.
}
public String getAssociateName() {
return associateName;
}
public void setAssociateName(String associateName) {
this.associateName = associateName;
}
public String getWorkStatus() {
return workStatus;
}
public void setWorkStatus(String workStatus) {
this.workStatus = workStatus;
}
public int tracksAssociateStatus() {
// TODO write logic here
return 1; // TODO change to whatever you need to return
}
}
You were specifying int for getAssociateName, when associateName is a String. This won't work; you need your getter return type to be the same as your field data type, or you need to convert the data to the method's return type. (The former is best practice).
Constructors don't specify a type, the class name is used and the compiler will understand what you want to do (which is return a new instance of the class). Therefore, your void associate() will tell the compiler "create a method called associate that doesn't return anything".

Well, would be nice if you provide the error itself for us.
But meanwhile, have you notice that your tracksassociatestatus method recieves an integer parameter days, and your constructor passes nothing to it?
So try changing your constructor to be something like:
Public associate() {
getassociatename();
setassociatename();
getworkstatus();
tracksassociatestatus(10);
setworkstatus();
}
For a cleaner code, check the other answer.
If you still have errors, please share them.

import java.util.*;
public class Associate
{
private String associateName;
private int workStatus;
private int days;
Scanner sc = new Scanner(System.in);
public String getAssociateName()
{
System.out.println("Enter the Associate id:");
associateName = sc.nextLine();
return associateName;
}
public void setassociatename(int associatename)
{
this.associateName=associateName;
}
public String tracksAssociatename()
{
return associateName;
}
public int getWorkStatus()
{
System.out.println("Enter the number of days");
days = sc.nextInt();
return days;
}
public void setWorkStatus(String workStatus)
{
this.workStatus=workStatus;
}
enter code here
public `enter code here`int tracksAssociateStatus()
{
return days;
}
public static void main(String args[])
{
Associate obj = new Associate();
obj.getAssociateName();
obj.getworkstatus();
System.out.println("The Associate name "+obj.tracksAssociatename()+" work Status "+obj.tracksAssociateStatus());
}
}

Why can't I seem to find the error in my program when compiling. Help needed

The pet store program should start with the user being able to choose to adopt a pet or give a pet the to the shop. If the user wants to adopt a pet, they should be able to see either all available pets, unless they say they know what type of pet they want, then show only available pets of that type.
The 4 methods that will need to be created for this program should:
add new pets
get a pet adopted
show pets by type
show pets available for adoption
Object Class: Pets.java
import java.util.*;
public class Pets {
public static void main(String[] args){
private double age; // age of the animal (e.g. for 6 months the age would be .5)
private String petName; // name of the animal
private String aType; // the type of the pet (e.g. "bird", "dog", "cat", "fish", etc)
private int collarID; // id number for the pets
private boolean isAdopted = false; // truth of if the pet has been adopted or not
private String newOwner;
private Date adoptionDate;
public double getAge() {
return age;
}
public void setAge(double age) {
this.age = age;
}
public String getPetName() {
return petName;
}
public void setPetName(String petName) {
this.petName = petName;
}
public String getaType() {
return aType;
}
public void setaType(String aType) {
this.aType = aType;
}
public int getCollarId() {
return collarID;
}
public void setCollarId(int collarId) {
this.collarID = collarId;
}
public boolean isAdoptated() {
return isAdopted;
}
public void setAdoptated(boolean isAdoptated) {
this.isAdopted = isAdoptated;
}
public Date getAdoptionDate() {
return adoptionDate;
}
public void setAdoptionDate(Date adoptionDate) {
this.adoptionDate = adoptionDate;
}
#Override
public String toString() {
return "Pets [age=" + age + ", petName=" + petName + ", aType=" + aType + ", collarId=" + collarID
+ ", isAdoptated=" + isAdopted + ", adoptionDate=" + adoptionDate + "]";
}
}
}

You should define the data fields and methods inside the class, but not inside the main()-method. The main()-method is the entry point of your java application and could be used to create an instance of your Pets class.
e.g.:
public static void main(String[] args) {
Pets pet = new Pets();
}

This code is not compiling for 2 main reasons:
You are specifying access modifiers on variables inside a method (in this case main), which is forbidden;
You are writing methods (e.g. getAge) inside another method (main) and trying to return a variable (e.g. age) that is out of that scope, in fact the variable age is not known inside the getAge method, because it's declared in the main method.
You should move the variable declaration to class level, and then have all methods separated using those variables. I'll give you a sketch, not the complete solution:
import java.util.*;
public class Pets {
/* Insert all variable declarations here */
private double age;
/* Constructor if you need it */
public Pets(/* parameters you think you need */) {
// Set attributes when you declare a new Pets()
}
/* Insert all methods you need here */
public double getAge() {
return this.age;
}
The positioning of the main method - for what I've understoon from your description - should be placed outside this class, in another class where the whole application will start to run. The Pet class should serve only for anything concerning pets (the four methods you will need to implement and all getters/setters for retrieving private class variables).

You’ve happened to put about everything — private fields and public methods — inside you main method. That doesn’t make sense. Everything that is in your main, move it outside, right under the line public class Pets {. That should fix your compiler error.

Having trouble with MAIN please advise [duplicate]

This question already has answers here:
"Error: Main method not found in class MyClass, please define the main method as..."
(10 answers)
Closed 9 years ago.
Sorry guys I am new to Java and I have an issue with my code. I have read through the threads and have seen many examples regarding this specific error (java.lang.NoSuchMethodError: main Exception in thread "main"). I just cant seem to wrap my head around where I would add (static void main(String[] args)) to the code. If you guys can point me in the right direction I would really appreciate it.
Here is what I have:
public class Employee {
String name;
String department;
double hourlyRate;
Employee(String name, String department, double hourlyRate) {
this.name = name;
this.department = department;
this.hourlyRate = hourlyRate;
}
public void setDepartment(String department) {
this.department = department;
}
public void setHourlyRate(double hourlyRate) {
this.hourlyRate = hourlyRate;
}
public String getNameAndDepartment() {
return name + " " + department;
}
double weeklyPay(int numOfHourWorked) {
if (numOfHourWorked < 40) {
return (numOfHourWorked * hourlyRate);
} else
return (40 * hourlyRate);
}
}
class UnionEmployee extends Employee {
double dues;
UnionEmployee(String name, String department, double hourlyRate, double dues) {
super(name, department, hourlyRate);
this.dues = dues;
}
public void setDues(double dues) {
this.dues = dues;
}
double weeklyPay(int numOfHourWorked) {
if (numOfHourWorked <= 40) {
return (super.weeklyPay(numOfHourWorked));
} else
return ((super.weeklyPay(40) + ((numOfHourWorked - 40) * hourlyRate * 1.5)) - dues);
}
}
class CommissionEmployee extends Employee {
double commisionRate;
double salesAmount;
CommissionEmployee(String name, String department, double hourlyRate) {
super(name, department, hourlyRate);
}
public void setCommisionRate(double commisionRate) {
this.commisionRate = commisionRate;
}
public void setSalesAmount(double salesAmount) {
this.salesAmount = salesAmount;
}
double weeklyPay(int numOfHourWorked) {
return (super.weeklyPay(numOfHourWorked) + (commisionRate * salesAmount));
}
}
class TestEmployee {
UnionEmployee uEmp = new UnionEmployee(null, null, 0, 0);
CommissionEmployee cEmp = new CommissionEmployee(null, null, 0);
Employee emp = new Employee(null, null, 0);
void display(Employee emp, int numOfHourWorked) {
System.out.println("Name and department :" + emp.getNameAndDepartment ());
System.out.println("Weekly pay of employee :"
+ emp.weeklyPay(numOfHourWorked));
}
void display(UnionEmployee uEmp, CommissionEmployee cEmp,
int numOfHourWorked) {
System.out.println("Weekly Pay for UnionEmployee"
+ uEmp.weeklyPay(numOfHourWorked));
System.out.println("Weekly Pay for UnionEmployee"
+ cEmp.weeklyPay(numOfHourWorked));
}
}
OK so I started by separating each class into a different file. In looking through the Java tutorials it said to add static void main(String[] args) the way the tutorial had it setup was like this:
public class Misc {
static void main(String[] args) {
//body
}
}
So I did this:
class TestEmployee {
static void main(String[] args) {
UnionEmployee uEmp = new UnionEmployee(null, null, 0, 0);
CommissionEmployee cEmp = new CommissionEmployee(null, null, 0);
Employee emp = new Employee(null, null, 0);
void display(Employee emp, int numOfHourWorked) {
System.out.println("Name and department :" + emp.getNameAndDepartment ());
System.out.println("Weekly pay of employee :"
+ emp.weeklyPay(numOfHourWorked));
}
void display(UnionEmployee uEmp, CommissionEmployee cEmp,
int numOfHourWorked) {
System.out.println("Weekly Pay for UnionEmployee"
+ uEmp.weeklyPay(numOfHourWorked));
System.out.println("Weekly Pay for UnionEmployee"
+ cEmp.weeklyPay(numOfHourWorked));
}
}
}
Still get the same error : (java.lang.NoSuchMethodError: main Exception in thread "main").
OK I add public but now I get this:
Exception in thread "main" java.lang.Error: Unresolved compilation problems:
void is an invalid type for the variable display
Syntax error on token "(", ; expected
Duplicate local variable emp
Syntax error on token ",", ; expected
Syntax error on token ")", ; expected
void is an invalid type for the variable display
Syntax error on token "(", ; expected
Duplicate local variable uEmp
Syntax error on token ",", ; expected
Duplicate local variable cEmp
Syntax error on token ",", ; expected
Duplicate local variable numOfHourWorked
Syntax error on token ")", ; expected
at TestEmployee.main(TestEmployee.java:9)

Your problem with main is that it doesn't exist, and you need to put one in your program for it to run. Put it in the main class, whichever one that is, but while it needs to be inside of the class, inside of the curly braces that define the class, you must also make sure that you don't put it inside of another method.
Above, I'd put it in TestEmployee.
I'd also take care to make sure every class above is declared public and is in its own file. So your code above which contains 4 classes, should be comprised of 4 files.
Edit
Also, be sure to declare your main method as a public method as #Aniket noted in comment below.
Edit 2
You're still not declaring main as a public method.
You have methods embedded within the main method. Remember that in Java you can't do this since all methods need to be class level. Get them out of the main method.
Your code indentation is horrible to say the least, and this will make it very difficult for you or us to see your coding problems. You will want to invest time and effort towards indenting your code properly. If you did this, you would see in an instant that you had methods inside of methods.

Java-How do I call a class with a string?

I am a beginner programmer and this is my first question on this forum.
I am writing a simple text adventure game using BlueJ as a compiler, and I am on a Mac. The problem I ran into is that I would like to make my code more self automated, but I cannot call a class with a string. The reason I want call the class and not have it all in an if function is so that I may incorporate more methods.
Here is how it will run currently:
public class textadventure {
public method(String room){
if(room==street){street.enterRoom();}
}
}
public class street{
public enterRoom(){
//do stuff and call other methods
}
}
The if statement tests for every class/room I create. What I would like the code to do is automatically make the string room into a class name that can be called. So it may act like so:
Public method(string room){
Class Room = room;
Room.enterRoom();
}
I have already looked into using Class.forName, but all the examples were too general for me to understand how to use the function. Any help would be greatly appreciated, and if there is any other necessary information (such as more example code) I am happy to provide it.
-Sebastien
Here is the full code:
import java.awt.*;
import javax.swing.*;
public class Player extends JApplet{
public String textOnScreen;
public void start(){
room("street1");
}
public void room(String room){
if(room=="street1"){
textOnScreen=street1.enterRoom();
repaint();
}
if(room=="street2"){
textOnScreen=street2.enterRoom();
repaint();
}
}
public void paint(Graphics g){
g.drawString(textOnScreen,5,15);
}
}
public abstract class street1
{
private static String textToScreen;
public static String enterRoom(){
textToScreen = "You are on a street running from North to South.";
return textToScreen;
}
}
public abstract class street2
{
private static String textToScreen;
public static String enterRoom(){
textToScreen = "You are on another street.";
return textToScreen;
}
}

Seeing as you are rather new to programming, I would recommend starting with some programs that are simpler than a full-fledged adventure game. You still haven't fully grasped some of the fundamentals of the Java syntax. Take, for example, the HelloWorld program:
public class HelloWorld {
public static void main(String[] args) {
String output = "Hello World!"
System.out.println(output);
}
}
Notice that public is lowercased. Public with a capital P is not the same as public.
Also notice that the String class has a capital S.* Again, capitalization matters, so string is not the same as String.
In addition, note that I didn't have to use String string = new String("string"). You can use String string = "string". This syntax runs faster and is easier to read.
When testing for string equality, you need to use String.equals instead of ==. This is because a == b checks for object equality (i.e. a and b occupy the same spot in memory) and stringOne.equals(stringTwo) checks to see if stringOne has the same characters in the same order as stringTwo regardless of where they are in memory.
Now, as for your question, I would recommend using either an Enum or a Map to keep track of which object to use.
For example:
public class Tester {
public enum Location {
ROOM_A("Room A", "You are going into Room A"),
ROOM_B("Room B", "You are going into Room B"),
OUTSIDE("Outside", "You are going outside");
private final String name;
private final String actionText;
private Location(String name, String actionText) {
this.name = name;
this.actionText = actionText;
}
public String getActionText() {
return this.actionText;
}
public String getName() {
return this.name;
}
public static Location findByName(String name) {
name = name.toUpperCase().replaceAll("\\s+", "_");
try {
return Enum.valueOf(Location.class, name);
} catch (IllegalArgumentException e) {
return null;
}
}
}
private Location currentLocation;
public void changeLocation(String locationName) {
Location location = Location.findByName(locationName);
if (location == null) {
System.out.println("Unknown room: " + locationName);
} else if (currentLocation != null && currentLocation.equals(location)) {
System.out.println("Already in room " + location.getName());
} else {
System.out.println(location.getActionText());
currentLocation = location;
}
}
public static void main(String[] args) {
Tester tester = new Tester();
tester.changeLocation("room a");
tester.changeLocation("room b");
tester.changeLocation("room c");
tester.changeLocation("room b");
tester.changeLocation("outside");
}
}
*This is the standard way of formating Java code. Class names are PascalCased while variable names are camelCased.

String className=getClassName();//Get class name from user here
String fnName=getMethodName();//Get function name from user here
Class params[] = {};
Object paramsObj[] = {};
Class thisClass = Class.forName(className);// get the Class
Object inst = thisClass.newInstance();// get an instance
// get the method
Method fn = thisClass.getDeclaredMethod(fnName, params);
// call the method
fn.invoke(inst, paramsObj);

The comments below your question are true - your code is very rough.
Anyway, if you have a method like
public void doSomething(String str) {
if (str.equals("whatever")) {
// do something
}
}
Then call it like
doSomething("whatever");

In Java, many classes have attributes, and you can and will often have multiple instances from the same class.
How would you identify which is which by name?
For example
class Room {
List<Monster> monsters = new ArrayList <Monster> ();
public Room (int monstercount) {
for (int i = 0; i < monstercount; ++i)
monsters.add (new Monster ());
}
// ...
}
Monsters can have attributes, and if one of them is dead, you can identify it more easily if you don't handle everything in Strings.