Java 認定試験で Var を利用するための ips

Java certification exams require a deep understanding of the language and its various features, including the use of var for local variable type inference. While this may seem like a small detail, it can greatly impact your code readability and efficiency. To help you ace your Java certification exam, here are four tips for utilizing var in your code:

1. Utilize var in enhanced for-loops: Looping through collections can often result in messy code due to the length of the loop control variable. Using var for the loop control variable can simplify the code and make it easier to read.

Use var for enhanced for-loops:

// ORIGINAL
for (List<String> list : listOfLists) {
    for (String str : list) {
        System.out.println(str);
    }
}
Using var for the loop control variable can simplify the code:
for (var list : listOfLists) {
    for (var str : list) {
        System.out.println(str);
    }
}

2. Simplify removing matching entries from a Map: Removing matching entries from a Map can be cumbersome and verbose when using wildcard type bounds and explicit type declarations. Employing var in your code can greatly simplify this process and improve readability.

Use var for removing matching entries from a Map:

// ORIGINAL
void removeMatches(Map<? extends String, ? extends Number> map, int max) {
    for (Iterator<? extends Map.Entry<? extends String, ? extends Number>> iterator =
            map.entrySet().iterator(); iterator.hasNext();) {
        Map.Entry<? extends String, ? extends Number> entry = iterator.next();
        if (max > 0 && matches(entry)) {
            iterator.remove();
            max--;
        }
    }
}
Using var can simplify this code:
void removeMatches(Map<? extends String, ? extends Number> map, int max) {
    for (var iterator = map.entrySet().iterator(); iterator.hasNext();) {
        var entry = iterator.next();
        if (max > 0 && matches(entry)) {
            iterator.remove();
            max--;
        }
    }
}

3. Use var in try-with-resources statements: In scenarios where multiple intermediate objects need to be declared in a try-with-resources statement, using var reduces clutter and makes the code more concise and understandable.

Use var in try-with-resources statements:

// ORIGINAL
try (InputStream is = socket.getInputStream();
    InputStreamReader isr = new InputStreamReader(is, charsetName);
    BufferedReader buf = new BufferedReader(isr)) {
    return buf.readLine();
}
Using var can reduce clutter and improve readability:
try (var inputStream = socket.getInputStream();
    var reader = new InputStreamReader(inputStream, charsetName);
    var bufReader = new BufferedReader(reader)) {
    return bufReader.readLine();
}

4. Simplify complex code with var: When faced with complex code where the type of a variable is difficult to comprehend, using var can significantly simplify the code for better understanding.

Use var for simplifying complex code:

// ORIGINAL
Map<List<String>, Map<Integer, List<String>>> complexMap = new HashMap<List<String>, Map<Integer, List<String>>>();
var complexMap = new HashMap<List<String>, Map<Integer, List<String>>>();

In conclusion, incorporating var in your Java certification exam can not only save you time and reduce code clutter, but also help you strategically simplify complex code and make it more readable. Keep these tips in mind when utilizing var in your code and you'll be well on your way to passing your Java certification exam with flying colors.

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