嵌套与GOTO：哪个最好避免？

#1 楼

public final class Pair {
    private String key;
    private String value;

    public Pair(key, value) {
        // TODO: Add proper argument checking/throw exceptions.

        this.key = key;
        this.value = value;
    }

    public String getKey() {
        return key;
    }

    public String getValue() [
        return value;
    }

    /**
     * Returns the string representation which looks like @{code key=value}.
     */
    @Override
    public String toString() {
        return key + "=" + value;
    }
}

/**
 * Constructs a Pair from the given string,
 * returns null if the string is misformed or
 * the string was null.
 * 
 * A well formed input looks like {@code key=value} and
 * does not start with a {@code #} as that indicates comments.
 */
public static Pair fromString(String str) {
    // We do not accept nulls and empty strings.
    if (str == null || str.empty()) {
        return null;
    }

    // TODO: Figure out if trimming of str would be a good idea.

    // Skip comments.
    if (str.startsWith("#")) {
        return null;
    }

    String[] splitted = str.split("=");

    // We also do not accept anything else.
    if (splitted.length != 2) {
        return null;
    }

    // TODO: Are you accepting zero-length keys/values?

    return new Pair(splitted[0], splitted[1]);
}

for (String line : lines) {
    Pair pair = Pair.fromString(line);
    if (pair != null && !values.containsKey(pair.getKey())) {
        // TODO
    }
}

#2 楼

#3 楼

for(String line : lines) {

     if(line.charAt(0) == '#') {
         ....

#4 楼

enum Validator {
    IsNotComment("Skipping commented line in file.") {

        @Override
        boolean isValid(String s) {
            return !s.startsWith("#");
        }

    },
    IsAPair("Not a pair") {

        @Override
        boolean isValid(String s) {
            return s.trim().split("=").length == 2;
        }

    };

    abstract boolean isValid(String s);

    public final String failMsg;

    Validator(String failMsg) {
        this.failMsg = failMsg;
    }
}

public void test() {
    String[] lines = {"Hello"};
    Map<String,String> values = new HashMap<>();
    for (String line : lines) {
        boolean valid = true;
        String failMsg = "";
        for ( Validator v : Validator.values() ) {
            valid &= v.isValid(line);
            if ( !valid ) {
                failMsg = v.failMsg;
            }
        }
        if ( valid ) {
            // Do stuff with valid lines.
            String [] parts = line.trim().split("=");
            values.add(parts[0],parts[1]);
        } else {
            System.out.println("Failed validation: "+failMsg);
        }
    }
}

List<String> lines = Arrays.asList(
        "# Comment",
        "",
        "A=B",
        "A=C",
        "X=Y ",
        "P = Q");

public void test() {
    Map<String,String> values = new HashMap<>();
    lines.stream()
            // Trim it and lowercase.
            .map(s -> s.trim().toLowerCase())
            // Discard empty lines - good call @rolfl
            .filter(s -> !s.isEmpty())
            // Discard comments.
            .filter(s -> s.charAt(0) != '#')
            // Split the trimmed form
            .map(s -> s.split("="))
            // Must be two parts.
            .filter(a -> a.length == 2)
            // Trim each one.
            .map(a -> new String[]{a[0].trim(), a[1].trim()})
            // Not seen already.
            .filter(a -> !values.containsKey(a[0]))
            // Install in values.
            .forEach (a -> values.put(a[0], a[1]));
    System.out.println(values);
}

{p=q, a=b, x=y}

#5 楼

#6 楼

for(String line : lines) {
    AddLine(line, values);
    //...and so on with still more processing
}

void AddLine(String line, Map<String, String> values)
{
    if(line.charAt(0) == '#') {
        LOGGER.debug("Skipping commented line in file.");
        return;
    }

    line = line.trim().toLowerCase();
    String[] pair = line.split("=");

    if(pair.length != 2) {
        LOGGER.error("Skipping malformed line in file: " + line);
        return;
    }

    pair[0] = pair[0].trim();
    pair[1] = pair[1].trim();

    if(values.containsKey(pair[0])) {
        LOGGER.debug("Value is already assigned.");
        return;
    }

    values.put(pair[0], pair[1]);
}

#7 楼

processLines = insertInto dict
              . map trimPairs
              . filter notMalformed
              . map splitLine
              . filter notComment

#8 楼

#9 楼

#10 楼

#11 楼

for(String line : lines) {

    try {
        if(line.charAt(0) == '#') {
            throw new Exception("Skipping commented line in file.");
        }

        line = line.trim().toLowerCase();
        String[] pair = line.split("=");

        pair[0] = pair[0].trim();
        pair[1] = pair[1].trim();

        if(values.containsKey(pair[0])) {
            throw new Exception("Value is already assigned.");
        }

        values.put(pair[0], pair[1]);

        //...and so on with still more processing
    } catch (Exception e) {
        LOGGER.error("Skipping line in file: " + line + " " + e.getMessage());
    }
}