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Command line arguments [duplicate]

This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 5 years ago.
I've created a class called Human that works properly, it takes 2 arguments, age and name, to create a human.
To create a Human with command line arguments, I want to write
java Filename -H "Anna" 25
And it should create a Human with thatname="Anna", and thatage=25, where 25 is an int.
The code I've written is creating a list called Argument, and iterating through it to find -H. I need to do this because I'm going to be using this to create different classes later. I just need help with the syntax on the lines where I've written thename=, and theage=, because I don't know how to get the next item in list, and next-next item in list.
public static void main(String[] args) {
ArrayList<String> Argument = new ArrayList<String>();
for (String item: args) {
Argument.add(item);
}
for (String item2: Argument) {
if (item2 == "-H") {
thatname = Argument.get(item2+1)
thatage = Argument.get(item2+2)
Human person = new Human(thatname,thatage);
System.out.println(person);
}

Why not just loop the args?
for ( int i = 0; i < args.length; i++ ) }
if (args[i].equals("-H")) {
i++;
thatName = args[i];
i++;
thatAge = args[i];
}
}
You should add some code to catch if one does not follow the rules you have set. Probably not enough arguments or other things humans do at the keyboard...

thatname = Argument.get(Argument.indexOf(item2)+1);
thatage = Argument.get(Argument.indexOf(item2)+2);
OR you know that 1st element is -H, 2nd element is name and 3rd is age, so you can use below code directly
thatname = Argument.get(1);
thatage = Integer.parseInt(Argument.get(2));

Your code have some problems, let me explain them to you for your assistance.
You cannot compare Strings with == you have to use equals method
in the String to compare between two Strings.
You have to use this for loop for(int i = 0; i < Argument.size();
i++) syntax so that you can iterate from zero to the number of
items in the list.
get method in ArrayList take the index as parameter and return the value at that index.
You can add i += 2 to skip the next two iterations which will
return the name and age value of the human. (It is optional)
Here is the working code:
public static void main(String[] args) {
ArrayList<String> Argument = new ArrayList<String>();
for (String item: args) {
Argument.add(item);
}
String currentItem;
for (int i = 0; i < Argument.size(); i++) { // it will iterate through all items
currentItem = Argument.get(i); // getting the value with index;
if (currentItem.equals("-H")) {
String thatname = Argument.get(i+1);
String thatage = Argument.get(i+2);
i += 2; // Skipping 2 iterations of for loop which have name and age human.
Human person = new Human(thatname,thatage);
System.out.println(person);
}
}
}

You cannot iterate the list using String. When iterating a list you required a index number like list.get(indexNumber);
public static void main(String[] args) {
ArrayList<String> Argument = new ArrayList<String>();
for (String item: args) {
Argument.add(item);
}
for (int i=0;i<args.length;i++) {
if (args[i].trim().equals("-H")) {
i++;
thatname = Argument.get(i);
i++;
thatage = Argument.get(i);
Human person = new Human(thatname,thatage);
System.out.println(person.getName()+" "+person.getAge());
}

Why using array list when you can directly use args? and while you're having only two parameters don't use a for loop access them direclty.
One thing you should know is that String is an object in java so comparing two Strings with == sign will return false even if they have same value (== will compare the id of the object), you should use .equale() function to compare the value of the object.
Check out this code :
public static void main(String[] args) {
if(args.length>0)
{
try{
if (args[0].equals("-H")) {
Human person = new Human( args[1],args[2]);
System.out.println(person);
}
}catch(ArrayIndexOutOfBoundsException exception) {
System.out.println("error with parameters");
}
}else
System.out.println("No command");
}

Merge sort java.lang.StackOverflowError

I am working on a project for school and things are going well until i tried to perform a merge sort on my ArrayList.
It will run but then it errors out. The first error of many is Exception in thread "main" java.lang.StackOverflowError.
I have looked over the code and cant find out why the error is occurring.
It does give me a location ( line 74:first_half = mergeSort(first_half); ) but i don't see the issue.
public static void main(String[] args) throws IOException {
// URL url = new
// URL("https://www.cs.uoregon.edu/Classes/15F/cis212/assignments/phonebook.txt");
FileReader fileReader = new FileReader("TestSort.txt");
BufferedReader bufferReader = new BufferedReader(fileReader);
String entry = bufferReader.readLine();
// Scanner s = new Scanner(url.openStream());
// int count = 0;
while (entry != null) {
// String person = s.nextLine();
String phoneNum = entry.substring(0, 7);
String name = entry.substring(9);
PhonebookEntry newentry = new PhonebookEntry(name, phoneNum);
phoneBook.add(newentry);
entry = bufferReader.readLine();
}
// ********************Selection
// Sort*************************************
ArrayList<PhonebookEntry> sortList = new ArrayList<PhonebookEntry>(phoneBook);
for (int min = 0; min < sortList.size(); min++) {
for (int i = min; i < sortList.size(); i++) {
int res = sortList.get(min).getName().compareTo(sortList.get(i).getName());
if (res > 0) {
PhonebookEntry temp = sortList.get(i);
sortList.set(i, sortList.get(min));
sortList.set(min, temp);
}
}
}
for (PhonebookEntry sortentry : sortList) {
System.out.println(sortentry);
}
System.out.println(mergeSort(mergeSortList));
}
// *****************************merge sort******************************************
static int mergecounter = 0;
static ArrayList<PhonebookEntry> mergeSortList = new ArrayList<PhonebookEntry>(appMain.phoneBook);
public static ArrayList<PhonebookEntry> mergeSort(ArrayList<PhonebookEntry> mergeSortLists) {
if (mergeSortLists.size() == 1) {
return mergeSortLists;
}
int firstHalf = mergeSortLists.size() % 2 == 0 ? mergeSortLists.size() / 2 : mergeSortLists.size() / 2 + 1;
ArrayList<PhonebookEntry> first_half = new ArrayList<PhonebookEntry>(mergeSortLists.subList(0, firstHalf));
ArrayList<PhonebookEntry> mergeSortHalf2 = new ArrayList<PhonebookEntry>(
mergeSortLists.subList(first_half.size(), mergeSortLists.size()));
System.out.println(++mergecounter);
first_half = mergeSort(first_half);
mergeSortHalf2 = mergeSort(mergeSortHalf2);
return merge(first_half, mergeSortHalf2);
}
public static ArrayList<PhonebookEntry> merge(ArrayList<PhonebookEntry> first_half,
ArrayList<PhonebookEntry> mergeSortHalf2) {
ArrayList<PhonebookEntry> returnMerge = new ArrayList<PhonebookEntry>();
while (first_half.size() > 0 && mergeSortHalf2.size() > 0) {
if (first_half.get(0).getName().compareTo(mergeSortHalf2.get(0).getName()) > 0) {
returnMerge.add(mergeSortHalf2.get(0));
mergeSortHalf2.remove(0);
}
else {
returnMerge.add(first_half.get(0));
first_half.remove(first_half.get(0));
}
}
while (first_half.size() > 0) {
returnMerge.add(first_half.get(0));
first_half.remove(first_half.get(0));
}
while (mergeSortHalf2.size() > 0) {
returnMerge.add(mergeSortHalf2.get(0));
mergeSortHalf2.remove(mergeSortHalf2.get(0));
}
return returnMerge;
}
}

My opinion there is no error in code.
How so sure?
I ran you code in my environment and its executed without any error.
With the text file i found at https://www.cs.uoregon.edu/Classes/15F/cis212/assignments/phonebook.txt As input
and done a simple implementation for PhonebookEntry
Then why is this error?
First off all try to understand the error, I mean why StackOverflowError occur. As there are lots of I am not going to explain this
But please read the top answer of this two thread and i am sure you will know why this happen.
Thread 1: What is a StackOverflowError?
Thread 2: What actually causes a Stack Overflow error?
If you read those I hope you understand the summury is You Ran Out Of Memory.
Then why I didnt got that error: Possible reason is
In my environment I configured the jvm to run with a higher memory 1024m to 1556m (as eclipse parameter)
Now lets analyze your case with solution:
Input: you have big input here ( 50,000 )
To check you code try to shorten the input and test.
You have executed two algorithm in a sigle method over this big Input:
When a method execute all its varibles stay in the memory untill it complete its execution.
so when you are calling merge sort all previouly user vairables and others stay in the memory which can contribute to this situation
Now if you use separated method and call them from the main method like write an method for selection sort, all its used varible will go out of scope
and possibly be free (if GC collect them) after the selection sort is over.
So write two separated method for reading input file and selection sort.
And Please Please close() those FileReader and BufferedReader.
Get out of those static mehtod . Make them non static create and object of the class and call them from main method
So its all about code optimization
And also you can just increase the memory for jvm and test by doing like this java -Xmx1556m -Xms1024m when ruining the app in command line
BTW, Thanks for asking this this question its gives me something to think about

How to take single input in java

I'm trying to take input by using code int rs=Integer.parseInt(args[0]); but it throw exception ArrayOutOfBondException. Please help me code is below.I need to take input only one time in commandline argument
package techgig;
import java.util.*;
public class Techgig {
public static int ta[]={1,12,5,111,200,1000,10,9,6,7,4};
public static void main(String[] args) {
Vector v = new Vector();
// TODO code application logic here
System.out.println("Amount Mark has:");
System.out.println("=============================");//here is the code
int rs=Integer.parseInt(args[0]);
// int rs=50;
System.out.print("===============================");
//int a=0;
int count=0;
int min=0,temp,totalamount=0;
System.out.print("\nToys Available:{");
for(int a=0;a<ta.length;a++)
{
if(a!=0)
{
System.out.print(",");
}
System.out.print(ta[a]);
}
System.out.print("}\n");
System.out.println("Buy Maximum toys with maximum left");
for(int i=0;i<ta.length;i++)
{
// System.out.print("\t"+ ta[i]);
for( int j=i+1;j<ta.length;j++)
{
if(ta[j]<ta[i])
{
temp=ta[j];
ta[j]=ta[i];
ta[i]=temp;
}
// System.out.print("\t"+ ta[i]);
}
}
for(int k=0;k<ta.length;k++)
{
totalamount=min;
// System.out.print("\t"+ ta[k]);
min=min+ta[k];
if(min >rs)
{
break;
}
count=count+1;
v.add(ta[k]);
}
int sav=0;
sav=rs-totalamount;
//System.out.println("Amount Mark has:"+rs);
System.out.println("Output:{"+v.size()+","+sav+"}");
System.out.println("Explanation");
System.out.println("Maximum number of toys="+v.size()+""+v);
System.out.println("Saving="+sav);
}
}

You need to pass command line arguments while running java program.
If you don't pass any command line arguments then args will be empty array, that is with length 0. And accessing 0th element from empty array will throw ArrayIndexOutOfBoundsException.

If you want to use args[0] you need to pass command line arguments to the program. If you're running your program from an IDE, you will get the exception that you get.

Let the name of the class having your main method is MyClass.java Then you must run your program from command line like
java MyClass 12
Where 12 is the command line argument which you are passing to your program(you may try with different argument)
Note: When you will not pass any argument but access the args in your program then you will see this exception originating

Array in Method Header: error ']' expected (Java)

I'm quite new to arrays and methods, and I've been seeing this error recurring through several programs: error '[' expected.
In each occasion, it seems to correct itself as I adjust something else, but in this particular case, I am completely stumped.
By the way, I am using several methods and arrays to create a quiz (before you ask, yes, this is an assignment and I agree, a list is a better way to handle this data - but that is not an option).
It is possible that I am not passing the arrays correctly between methods, as I'm a little muddy on that process. From my understanding, in order to send/receive (i.e. import/export) an array or other variable between methods, I must declare that variable/array in the method header parameters.
import java.util.Scanner;
public class H7pseudo
{
public static void main(String[] args)
{
//call getAnswerkey method
getAnswerkey(answerkey[i]);
//call getAnswers method
getAnswers(answers[i]);
//call passed method? necessary or no?
boolean passed = passed(answerkey[i], answers[i], qMissed[i], points);
//Print results of grading
if (passed)
{
System.out.println("Congratulations! You passed.");
}
else
{
System.out.println("Try again, sucka. You FAILED.");
}
//call totalPoints
totalIncorrect(points);
//call questionsMissed
questionsMissed(qMissed[i]);
}
//get answer key (create answerkey array & export)
public static void getAnswerkey(answerkey[i])
{
//create answerkey array here
char[] answerkey;
//determine number of questions (indices)
answerkey = new char[20];
//input values (correct answers) for each index
//for our purposes today, the answer is always 'c'.
for (int i = 0; i <=20; i++)
{
answerkey[i] = 'c';
}
}
//get student answers (create answers array & export)
public static void getAnswers(answers[i])
{
//initialize scanner for user input
Scanner scan = new Scanner(System.in);
//create answer array here
char[] answers;
//determine number of questions (indices)
answers = new char[20];
//prompt for user input as values of each index
for (int i = 0; i <= 20; i++) {
answers[i] = scan.nextChar();
}
}
//grade student answers (import & compare index values of arrays:answers&answerkey
//create & export qMissed array
public static boolean passed(answerkey[i], answers[i], qMissed[i], points)
{
int points = 0;
//create new array: qMissed
boolean[] qMissed;
//determine number of questions to be graded
qMissed = new boolean[20];
//initialize values for array
for (int i = 0; i <= 20; i++) {
qMissed[i] = false;
}
//cycle through indices of answerkey[i] & answers[i];
for (int i = 0; i =< 20; i++)
{
if (answers[i] == answerkey[i])
{
correct = true;
points = points+1;
qMissed[i] = true;
}
else {
qMissed[i] = false;
}
}
//evaluate whether or not the student passed (15+ correct answers)
if (points >= 15)
{
passed = true;
}
else
{
passed = false;
}
return passed;
}
public static void totalIncorrect(points)
{
int missed = 20 - points;
System.out.println("You missed " + missed + " questions.");
}
public static void questionsMissed(qMissed[i])
{
// for each index of the array qMissed...
for (int i = 0; i < qMissed.length; i++)
{
//...print correct and false answers.
system.out.println(i + ": " + qMissed[i] + "\n");
}
}
}

You can't define array size in the method signature, in Java.

public static void getAnswerkey(answerkey[i])
You can't put anything inside the [] in a method declaration. Also, you have to mention the type:
public static void getAnswerKey(char[] answerkey)
This is not the only reason your code won't work as intended, but I'll leave the rest as part of the exercise.

Look at your method definitions:
public static void questionsMissed(qMissed[i])
This is wrong. You should define the type of the variable and it should not contain [i] like an element of an array. It should be something like this:
public static void questionsMissed(int qMissed)
Or if you want to pass the array, write it like this:
public static void questionsMissed(int[] qMissed)
Apart of this, there are other several errors in your code:
getAnswerkey(answerkey[i]); //answerkey is not defined
getAnswers(answers[i]); //answers is not defined
It would be better if you start reading a Java tutorial first.

I want to vote up Luiggi's answer, but I don't have enough reputation to do that :)
Congrats, cordivia, on getting started with Java!
Here is how an array is declared:
type[] arrayName = new type[numberOfElements]
For example, you did this right in your method definition for getAnswerkey():
char[] answerkey;
answerkey = new char[20];
The part in the method definition inside the parentheses defines the kind of data the method is willing to accept from the outside. So if you don't need to put something into the method to get something out of it, you don't need to put anything in the parentheses. Define the method like this:
getAnswerkey() {
...But that's not the whole story. If you want to get something out of the method, it needs to have a return type as well. A return type is what you're gonna get out of the method when the method's done doing it's magic. For example, if you want to get an int array out of a method you would do something like this:
public static int getTheInteger() {
Since you want an array of chars from the method, you'll want to do something like this:
public static char[] getAnswerkey() {
So that's how you get a method to give you something back. If don't want anything back, you put void:
public static void noMarshmallows() {
Now, when you use the method, you're gonna need to do something with what it gives you, or it did all that work for nothing. So you need to store the return value in a variable when you call the array (calling methods is what you've been doing in main). You know how to store something in a variable. You use the '=' operator:
int myVeryFavoriteNumber;
myVeryFavoriteNumber = 5;
So, you do the same thing when you're getting something out of an array. You assign the return value to a variable. If you want to do this with an array, do this:
int[] myFavs;
myFavs = getMyFavoriteNumbers();
Same with chars:
char[] answerKey;
answerKey = getAnswerKey();
Voila! Your answer key is now right out in the open for the rest of main to see :)
Now, if you want to put something into a method and have it do something with what you put in, you define a parameter. You know how this works. It's just like declaring a variable, and that's exactly what it is. Parameters go in the parentheses and only the method using the parameter sees that variable name (it's local). Something like this:
public static void plusOneToAll (int[] numbers) {
for (int i = 0; i < numbers.length; i++) {
numbers[i] = numbers[i] + 1;
}
}
Notice int[] numbers in the parentheses. The type being passed in is int[] or integer array. numbers is just the parameter name. It functions just like a variable, but it is declared locally (inside the parentheses) and use locally (inside the method). So, if you wanted to compare the answers from two arrays and return the number of matches (like a total score for instance), you would do something like this:
public static int getTotalScore (char[] correctAnswers, char[] userAnswers) {
int totalScore = 0;
for (int i = 0; i < correctAnswers.length; i++) {
if (userAnswers[i] == correctAnswers[i]) {
totalScore = totalScore + 1;
}
}
return totalScore;
}
Notice the return type: int (written before the method name). Inside the array I'm using the variable totalScore to keep track of the number of times the answers match. The method takes two char arrays from the outside and uses them on the inside. Finally, I return an int: totalScore. That kicks the value of totalScore back out to whatever called it (main).
If I might add one last thing: Do yourself a favor and go pick up a copy of Head First Java. It's hard to find a good tutorial online and Java textbooks are just plain boring. The Head First series are kind of like coloring books for adults.
Best of luck!

Adding a string to an arraylist through another arraylist's object's method

I am in the process of updating my game to Java, but the only minor bug I have left is this:
Every time a dead player's name is "added" to the dead player name list, it adds the Player object's hashcode instead.
EDIT: Here is a link to a zip folder with the source code:
https://dl.dropboxusercontent.com/u/98444970/KarmaSource.zip
The code in question is the two places where the line gets the player object and gets the object's name. When it is used in println, it works fine and prints the player's name. However, in the second part where it does the same thing, but it prints the hashcode of the player object instead of calling its get_name method and returning the String. I'm not sure if it has to do with the third part, where it adds the "name" to dead player list pdead.
If you'd like a link to the compiled version, let me know. It's compiled under JDK 7 Update 51 64-bit.
EDIT: I got it working, I was originally referencing the players list instead of the pdead list. Thanks to all who contributed to helping. If you still want the game, let me know and I'll put a download link :D

Answering your question:
This code is wrong:
if (karma.pdead.isEmpty())
{System.out.println("None");}
else
for (int index = 0;index < karma.pdead.size();index++)
System.out.println(pdead.get(index));
What is karma? Whatever that is, looks like you're referring to 2 different things there.
Try this:
if (pdead.isEmpty()) {
System.out.println("None");
} else {
for (String deadPlayer : pdead) {
System.out.println(deadPlayer);
}
}
Pretty sure this will work :)
Some further, constructive advice:
Your code is breaking pretty much all conventions/good-practices I know in Java. But I am here to help, not to criticize, so let's try to improve this code.
Never keep state in static fields. This is a recipe for causing memory leaks.
your main function won't even compile. Should look like this:
public static void main(String[] args)
Always wrap the body of for loops with braces.
Be consistent: if you open braces in a new line, then do it every time. NEVER write code on the same line as the opening bracket.
GOOD:
public void doSomething()
{
// body
}
GOOD:
public void doSomething() {
// body
}
BAD:
public void doSomething() {
// body
}
public void somethingOther()
{
// inconsistent!
}
public void terribleCode()
{ System.out.println("Never do this"); }
Do not use underscores to separate words. In Java, the favoured convention is to use camelCase. getName(), not get_name().
class names ALWAYS start with a capital letter, whereas variable names generally start with a lower-case letter.
if you're iterating over all items of a list, just use the forEach construct (shown above) not index navigation.

I wanted to check to see if there was some subtle syntax error, so I cut/paste your code into an editor and tried to massage it to get it running. After my massaging, I ran it and it ran fine. Here is the code I ran and the results I got:
Code:
import java.util.ArrayList;
public class Game {
private static ArrayList<Player> players = new ArrayList<Player>();
private static ArrayList<String> pdead = new ArrayList<String>();
public static void main(String[] args) {
// Some Test Data
Player p1 = new Player("George");
p1.setHp(10);
players.add(p1);
Player p2 = new Player("Bob");
p2.setHp(10);
players.add(p2);
// Print Current State of data
System.out.println("Current Players");
for(Player p: players) {
System.out.println(p.getName() + ": " + p.getHp());
}
System.out.println("Dead Players");
if (pdead.isEmpty()) {
System.out.println("None");
} else {
for (int index=0; index < pdead.size(); index++) {
System.out.println(pdead.get(index));
}
}
// Kill Bob
p2.setHp(0);
// Do work to add names to dead players data structure
for (int index2=0; index2 < players.size(); index2++) {
if ((players.get(index2).getHp() <= 0) && !(pdead.contains(players.get(index2).getName()))) {
pdead.add(players.get(index2).getName());
}
}
// Print Current State of data
System.out.println("Current Players");
for(Player p: players) {
System.out.println(p.getName() + ": " + p.getHp());
}
System.out.println("Dead Players");
if (pdead.isEmpty()) {
System.out.println("None");
} else {
for (int index=0; index < pdead.size(); index++) {
System.out.println(pdead.get(index));
}
}
}
}
class Player {
private String name = "";
private int hp = 0;
public Player(String n) {
name = n;
}
public String getName() {
return name;
}
public int getHp() {
return hp;
}
public void setHp(int h) {
hp = h;
}
}
Here are the results that code gives me:
javac Game.java
java Game
Current Players
George: 10
Bob: 10
Dead Players
None
Current Players
George: 10
Bob: 0
Dead Players
Bob