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NeXtMidas Training
File Handlers
Lab 1
Part 4
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- Part 4 - Listing:
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Now lets add the methods that will be used by commands like DATALIST when
listing elements from the file. For the most part these methods look very similar
when going from one file handler to the next.
- listElements(..) and listElementsPerLine(..)
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The listElementsPerLine(..) method tells datalist how many elements
to list on each line. This allows allows DATALIST to conserve vertical
space by listing multiple elements per line... we don't realy care about that
right now, so just return 1 telling it to display only one element per line.
public int listElementsPerLine (int lineWidth, String format, int flags) {
return 1;
}
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The listElements(..) method actually lists the elements. Again we will
go through it line-by-line.
public String listElements (double start, int elements, String format, int flags) {
Data data = getDataBuffer(elements); // 1
seek(start); // 2
int numRead = read(data, elements); // 3
if (numRead <= 0) return null; // 4
return data.toString(0, numRead, 10)+"\n"; // 5
}
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Line 1: Create a data buffer to use when reading in the data.
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Line 2: Seek to the start of the data we wantr to read.
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Line 3: Read in the data.
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Line 4: If there was nothing available to read (e.g. end-of-file),
just return null.
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Line 5: Convert the data to a string. In this case we are converting
to test starting at 0 with numElements total and using
base-10. By convention, this always has a newline character added
on to the end of the string.
- continued on next page
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