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Java

Posted by Eugenio Villarreal
Eugenio Villarreal
8,041 Points

Error: Exception in thread "main" java.util.IllegalFormatFlagsException: Flags = ' '

I can't get around this error: I searched online but could not figure out the issue.

Exception in thread "main" java.util.IllegalFormatFlagsException: Flags = ' '
at java.util.Formatter$FormatSpecifier.checkText(Formatter.java:3037)
at java.util.Formatter$FormatSpecifier.<init>(Formatter.java:2733)
at java.util.Formatter.parse(Formatter.java:2560)
at java.util.Formatter.format(Formatter.java:2501)
at java.io.PrintStream.format(PrintStream.java:970)
at java.io.PrintStream.printf(PrintStream.java:871)
at Example.main(Example.java:22) 

import java.util.Arrays;
import java.util.Date;
import java.util.HashSet;
import java.util.Set;

import com.teamtreehouse.Treet;
import com.teamtreehouse.Treets;


public class Example {

  public static void main(String[] args) {
    Treet[] treets = Treets.load();
    System.out.printf("There are %d treets. %n",
                     treets.length); 
    Set<String> allHashTags = new HashSet<String>();
    Set<String> allMentions = new HashSet<String>();
    for (Treet treet : treets){
      allHashTags.addAll(treet.getHashTags());
      allMentions.addAll(treet.getMentions());
    }
    System.out.printf("Hash tags: s% %n", allHashTags);
    System.out.printf("Mentions: s% %n", allMentions);
  }

}

package com.teamtreehouse;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Date;
import java.util.List;

public class Treet implements Comparable<Treet>, Serializable {
  private static final long serialVersionUID = 7146681148113043748L;
  private String mAuthor;
  private String mDescription;
  private Date mCreationDate;

  public Treet(String author, String description, Date creationDate) {
    mAuthor = author;
    mDescription = description;
    mCreationDate = creationDate;
  }

  @Override
  public String toString() {
    return String.format("Treet:  \"%s\" by %s on %s", 
                         mDescription, mAuthor, mCreationDate);
  }

  @Override
  public int compareTo(Treet other) {
    if (equals(other)) {
      return 0;
    }
    int dateCmp = mCreationDate.compareTo(other.mCreationDate);
    if (dateCmp == 0) {
      return mDescription.compareTo(other.mDescription);
    }
    return dateCmp;
  }

  public String getAuthor() {
    return mAuthor;
  }

  public String getDescription() {
    return mDescription;
  }

  public Date getCreationDate() {
    return mCreationDate;
  }

  public List<String> getWords() {
   String[] words = mDescription.toLowerCase().split("[^\\w#@']+");
   return Arrays.asList(words);

  }

  public List<String> getHashTags(){ 
    return getWordsPrefixedWith("#");      
  }

  public List<String> getMentions(){
    return getWordsPrefixedWith("@");
  }

  private List<String> getWordsPrefixedWith(String prefix) {
    List<String> result = new ArrayList<String>();
    for (String word : getWords()) {
      if(word.startsWith(prefix)){
      result.add(word);
      }
    }
  return result;  
  }
}

1 Answer

Simon Coates
Simon Coates
28,695 Points

documentation on the printf method (https://docs.oracle.com/javase/7/docs/api/java/io/PrintStream.html#printf(java.lang.String,%20java.lang.Object...) ) includes mention that it can throw:

IllegalFormatException - If a format string contains an illegal syntax, a format specifier that is incompatible with the given arguments, insufficient arguments given the format string, or other illegal conditions. For specification of all possible formatting errors, see the Details section of the formatter class specification.

So check your placeholders, and then test that they are appropriate for the arguments passed in.

Update. I ran a quick demo:

import java.util.HashSet;
import java.util.Set;

class Main {
  public static void main(String[] args) {

    Set<String> allHashTags = new HashSet<String>();
    allHashTags.add("fun");
    allHashTags.add("mercury");

    System.out.printf("Hash tags: %s %n", allHashTags);

    System.out.println("Or maybe something like");
    int n = 1;
    for(String tag : allHashTags)
    {
      System.out.printf("%d) %s %n", n, tag);
      n++;
    }
  }
}

produces:

Hash tags: [mercury, fun] 
Or maybe something like
1) mercury 
2) fun
Eugenio Villarreal
Eugenio Villarreal
8,041 Points

Ha, I thought I checked it but once again I miss-typed %s , I typed s%. This has become a common mistake for me. Thanks for pointing it out, I ket reading through it.

Simon Coates
Simon Coates
28,695 Points

Java's standard library has good documentation compared to other programming languages and the exceptions are usually a decent indication of what's gone wrong. Getting placeholders wrong is an easy mistake to make (I always forget which symbol it's meant to be).