Lab3Help

Class External

java.lang.Object

Lab3Help.External

All Implemented Interfaces:

Path<String>

public class External
extends Object
implements Path<String>

Implements the Path interface by calling an external program.

This program must take four arguments:

1. A stop file.
2. A line file.
3. The point of departure.
4. The point of arrival.

If a shortest path is found, then the program must produce output in the following format:

1. The number of minutes required to perform the trip (a decimal number).
2. Every stop along the way, including the points of departure and arrival.

If no shortest path is found, then the program must produce output in a format that cannot be confused with the format given above.

Constructor Summary

Constructors

Constructor and Description
External(List<BStop> stops, List<BLineTable> lines) Creates an instance of this class for the program Lab3 (or, if the use of Lab3 fails in certain ways, Lab3.bat) in the current directory and the transport network defined by stops and lines.
External(String program, List<BStop> stops, List<BLineTable> lines) Creates an instance of this class for the program program (or, if the use of program fails in certain ways, program + ".bat") and the transport network defined by stops and lines.

Method Summary

Modifier and Type	Method and Description
void	computePath(String from, String to) Computes the path from from to to (if any).
Iterator<String>	getPath() Returns an iterator over the nodes in the path.
int	getPathLength() Returns the length of the computed path, that is, the sum of the weights of each arc on the path.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

External

public External(String program,
                List<BStop> stops,
                List<BLineTable> lines)

Creates an instance of this class for the program program (or, if the use of program fails in certain ways, program + ".bat") and the transport network defined by stops and lines.

Preconditions: The program must accept input and produce output in a certain format (see External). All stop names must be unique. All stop names in lines must also exist in stops.

External

public External(List<BStop> stops,
                List<BLineTable> lines)

Creates an instance of this class for the program Lab3 (or, if the use of Lab3 fails in certain ways, Lab3.bat) in the current directory and the transport network defined by stops and lines.

Preconditions: The program must accept input and produce output in a certain format (see External). All stop names must be unique. All stop names in lines must also exist in stops.

Method Detail

computePath

public void computePath(String from,
                        String to)

Description copied from interface: Path

Computes the path from from to to (if any). Path information can be retrieved by subsequent calls to getPath() and getPathLength(). It must be possible to call this method any number of times.

Precondition: The underlying graph must not contain any negative edge weights.

Specified by:

computePath in interface Path<String>

getPath

public Iterator<String> getPath()

Description copied from interface: Path

Returns an iterator over the nodes in the path.

If a path has been found the first node in the iterator is the argument from passed to computePath and the last node is to.

If no path was found or if no call to computePath has been made the iterator is empty.

Specified by:

getPath in interface Path<String>

Returns:

An iterator over the computed path.

getPathLength

public int getPathLength()

Description copied from interface: Path

Returns the length of the computed path, that is, the sum of the weights of each arc on the path.

If no path was found the return value is an arbitrary integer. It is appropriate but not required to return a special value such as -1 in this case.

Specified by:

getPathLength in interface Path<String>

Returns:

The length of the computed path.