Sorting string value in a case-insensitive manner in Java 8

问题

How do I sort string values in case-insensitive order in the following?

List<Employee> listofEmployees = Arrays.asList(
    new Employee(1, "aaa", Arrays.asList(123, 345, 678)),
    new Employee(1, "bbb", Arrays.asList(91011, 121314, 1516117)),
    new Employee(2, "ccc", Arrays.asList(181920, 212223, 242526)),
    new Employee(3, "ddd", Arrays.asList(272829, 303132, 333435)),
    new Employee(4, "BBB", Arrays.asList(29, 332, 33))
);

I wrote like this:

listofEmployees.stream().sorted(Comparator.comparing(Employee::getName).reversed())
        .forEach(s -> System.out.println(s.getName()));

How do I pass a string case insensitive option here?

回答1:

Try this

Comparator.comparing(Employee::getName, String.CASE_INSENSITIVE_ORDER)

回答2:

As @Tree suggested in comments, one can use the java.text.Collator for a case-insensitive and locale-sensitive String comparison. The following shows how both case and accents could be ignored for US English:

Collator collator = Collator.getInstance(Locale.US);
collator.setStrength(Collator.PRIMARY);
listOfEmployees.sort(Comparator.comparing(Employee::getName, collator.reversed()));

When collator strength is set to PRIMARY, then only PRIMARY differences are considered significant during comparison. Therefore, the following Strings are considered equivalent:

if (collator.compare("abc", "ABC") == 0) {
    System.out.println("Strings are equivalent");
}

回答3:

You can specify it as the second argument to ignore cases:

Comparator.comparing(Employee::getName, String::compareToIgnoreCase).reversed()

回答4:

This is one of many ways:

listofEmployees.stream()
    .sorted((o1, o2) -> o1.getName().compareToIgnoreCase(o2.getName()))
    .forEach(s -> System.out.println(s.getName()));

回答5:

It looks like there is a Comparator that orders String objects as by compareToIgnoreCase, you can read the documentation here: https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#CASE_INSENSITIVE_ORDER

回答6:

You can lowercase or uppercase it like this:

listofEmployees.stream()
               .sorted(Comparator.comparing((Employee e) -> e.getName()
                                 .toLowerCase()) // or toUpperCase
                                 .reversed())
               .forEach(s -> System.out.println(s.getName()));

来源：https://stackoverflow.com/questions/49821774/sorting-string-value-in-a-case-insensitive-manner-in-java-8

标签

java

java-8

java-stream