Using the contains method on an ArrayList of ArrayLists

[Matthew Busse]

Hello Java ranchers,

I'm in a pickle. I need to check if an ArrayList of ArrayLists contains a string, and if it does, continue onto the next iteration of a for loop. However, I don't think using the .contains method on the ArrayList of ArrayLists checks through all the individual items of the individual ArrayLists, at least it doesn't appear to do do in the tests I've run. So I tried using the contains method on the individual ArrayLists, but to do that, I need to put it within an iterator or a for loop or something, and then the continue method only continues that small for loop, not the bigger for loop, so I don't know how to do this.

Here's what I want to do, the problem line is pointed out with comments:

public List<List<String>> sourceFileParametersParser(List<String> linesFromSourceFile) {
		
		
		
		List<List<String>> epParametersArray = new ArrayList<List<String>>();
		
		for ( int i = 3; i < linesFromSourceFile.size(); i++ ) {
		    
	    	List<String> epParameters = new ArrayList<String>(); 
			
			String[] fields = linesFromSourceFile.get(i).split("\t");
	    	
	    	String epitopeName = fields[1];
	    	String sequence = fields[2]; 
	    	String gINumber = fields[4]; 

	    	//this next line doesn't appear to actually check all the elements of the ArrayLists contained within the ArrayList
	    	if (epParametersArray.contains(epitopeName)){
	    		continue;
	    	}	
	    	
	    	epParameters.add(epitopeName);
	    	epParameters.add(sequence);
	    	epParameters.add(gINumber);
	    	
	    	epParametersArray.add(epParameters);
	    	
	    }	
		return epParametersArray;
	}

These following lines work for checking the elements of the ArrayLists contained in the ArrayList, but they have to be inside of some kind of loop, so a continue statement only continues that smaller loop:

for (int j = 0; j < epParametersArray.size(); j++) {
	    		if(epParametersArray.get(j).contains(epitopeName)) {
	    			continue;
	    		}
	    	}
	    	
	    	Iterator it = epParametersArray.iterator();
	    	while (it.hasNext()) {
	    		if(((ArrayList<String>)it.next()).contains(epitopeName)) {
	    			continue;
	    		}
	    	}  

Does anyone know a way around this?

Thanks,
Matt

[Jeanne Boyarsky]

Matt,
You are correct that you need to loop through the outer ArrayList. What if you used a helper method? Then you could use return instead of continue. (The alternative is a labeled continue which is horrible to read/maintain.)

For example:

private boolean nestedContains(ArrayList<?> outer) {
  for (ArrayList<?> inner : outer) {
    if ( inner.contains(whatever)) {
      return true;
   }
  }
  return false;
}

[Ernest Friedman-Hill]

"continue" without an argument will jump to the next go-round of the immediately enclosing loop. But it can actually be used to continue an outer loop, too, if you label the loop and then add the name of the label as an argument:

outer:
    for (int i=0; i<10; ++i)
        for (int j=0; j<10; ++j)
            if (something(i, j))
                continue outer;

[Matthew Busse]

Thank you for your responses Jeanne and Ernst.

Labeling the outer for loop seems like a really simple fix, is it really that bad to use labeled for loops?

This works:

public List<List<String>> sourceFileParametersParser(List<String> linesFromSourceFile) {
		
		//parses the input file, extracts the epitope name, peptide sequence, and GI number
		//creates ArrayList holding ArrayLists of the individual parameters. 
		
		List<List<String>> epParametersArray = new ArrayList<List<String>>();
		
		outer: for ( int i = 3; i < linesFromSourceFile.size(); i++ ) {
		    //Get the peptide sequence and suspected GI, add them to return list
			//starts at the 4th line because the first 3 are example text
	    	List<String> epParameters = new ArrayList<String>(); 
			
			String[] fields = linesFromSourceFile.get(i).split("\t");
	    	
	    	String epitopeName = fields[1];
	    	String sequence = fields[2]; 
	    	String gINumber = fields[4]; 
	    	
	    	for (int j = 0; j < epParametersArray.size(); j++) {
	    		if(epParametersArray.get(j).contains(epitopeName)) {
	    			continue outer;
	    		}
	    	}
	    	  	
	    	epParameters.add(epitopeName);
	    	epParameters.add(sequence);
	    	epParameters.add(gINumber);
	    	
	    	epParametersArray.add(epParameters);
	    	
	    }	
		return epParametersArray;
	}

[Campbell Ritchie]

Labelled break and labelled continue are equivalent to "goto". Many people believe goto is a potent source of errors in programming, but that is by no means a universal opinion.