Java подстановка в строку параметров

Как вставить переменную в строку java

Чтобы вставить переменную в строку Java , вы можете использовать оператор + для объединения строк и переменных.

Пример, используя оператор + :

String name = "Alice"; int age = 30; String message = "Привет, меня зовут " + name + " и мне " + age + " лет."; 

Есть также другой подход, который использует метод String.format() :

String name = "Bob"; int age = 25; String message = String.format("Привет, меня зовут %s и мне %d лет.", name, age); 

В этом примере мы использовали метод String.format() для создания строки message . В качестве первого аргумента мы передали шаблон строки с плейсхолдерами %s и %d , которые будут заменены значениями переменных, переданными вторым и последующими аргументами метода.

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String.format в Java

— Я еще хотела тебе рассказать о методе String.format в Java.

Это статический метод класса String , но очень полезный. Но начну издалека.

Когда тебе нужно вывести в одной строке текст, содержащий значения нескольких переменных, как ты будешь это делать?

String name = "Bender"; int age = 12; String friend = "Fry"; int weight = 200;

String name = "Bender"; int age = 12; String friend = "Fry"; int weight = 200; System.out.println("User = ");

— Не очень читаемо – не так ли?

— Но вот если имена переменных у тебя будут длинные или нужно будет вызывать методы для получения данных, будет уже не очень читаемо:

— Ну, если так, то да – не очень читаемо.

— Дело в том, что в реальных программах такое встречается очень часто, поэтому я хочу показать тебе, как можно упростить себе жизнь с помощью метода String.format.

— Да говори же скорее, что это за волшебный метод такой?

— Вот как можно записать приведенный выше код:

String text = String.format("User = ", user.getName(), user.getAge(), user.getFriends().get(0), user.getExtraInformation().getWeight()) System.out.println(text);

В метод String.format первым параметром передается строка-шаблон, в которой, на местах, в которые мы хотим подставить значения, стоят специальные символы: %s, %d.

После строки-шаблона передаются параметры, значения которых и будут подставлены на место символов %s, %d.

Если нужно подставить строку мы пишем %s, если число — %d.

String s = String.format("a = %d, b = %d, c = %d", 1, 4, 3);

s будет равна «a = 1, b = 4, c = 3»

— А ведь еще можно делать и так:

int a = -1, b = 4, c = 3; String template; if (a < 0) template = "Warning! a = %d, b = %d, c = %d"; else template = "a = %d, b = %d, c = %d"; System.out.println(String.format(template, a, b, c) );

— Гм. Действительно полезный метод, спасибо, Элли.

— Если ты хочешь использовать в методе format другие типы данных, то вот тебе таблица:

На самом деле у этих параметров еще есть свои настройки, а у них свои.

Но для начала тебе этого хватит. Если же нет – вот тебе ссылка на официальную документацию:

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String Interpolation in Java

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Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.

The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.

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We're looking for a new Java technical editor to help review new articles for the site.

1. Overview

In this tutorial, we'll discuss the topic of String interpolation in Java. We'll look at a few different examples, and then go through some of the details.

2. String Interpolation in Java

String interpolation is a straightforward and precise way to inject variable values into a string . It allows users to embed variable references directly in processed string literals. Java lacks native support for String interpolation in comparison to languages like Scala.

However, there are some approaches to accomplish this behavior in Java. In the following sections, we'll explain each one of these approaches.

3. Plus Operator

First, we have the “+” operator. We can use the “+” operator to concatenate our variables and string values. The variable is replaced by its value, so we achieve interpolation or concatenation of strings:

@Test public void givenTwoString_thenInterpolateWithPlusSign()

As we can see in the previous example, with this operator, the resulting String contains the values of the variables “interpolate” with other string values. Since it may be adjusted to fit specific needs, this string concatenation method is among the most straightforward and valuable. When using the operator, we don't need to put the text in quotations.

4. The format() Function

Another approach is using the format() method from the String class. Contrary to the “+” operator, in this case we need to use placeholders to get the expected result in the String interpolation:

@Test public void givenTwoString_thenInterpolateWithFormat()

Additionally, we can reference a specific argument if we want to avoid variable repetitions in our format call:

@Test public void givenTwoString_thenInterpolateWithFormatStringReference()

Now we've reduced unnecessary variable duplication, and instead used the index of the argument in the argument list.

5. StringBuilder Class

Our following approach is the StringBuilder class. We instantiate a StringBuilder object and then call the append() function to build the String. In the process, our variables are added to the resulting String:

@Test public void givenTwoString_thenInterpolateWithStringBuilder()

As we can see in the above code example, we may interpolate the strings with the necessary text by chaining the append function, which accepts the parameter as a variable (in this case, two Strings).

6. MessageFormat Class

Using the MessageFormat class is a lesser known method to obtain String interpolation in Java. With MessageFormat, we may create concatenated messages without worrying about the underlying language. It's a standard method for creating user-facing messages. It takes an object collection, formats the strings contained within, and inserts them into the pattern at the proper locations.

MessageFormat‘s format method is nearly identical to String‘s format method, except for how the placeholders are written. Indexes like , , , etc., represent the placeholder in this function:

@Test public void givenTwoString_thenInterpolateWithMessageFormat() < String EXPECTED_STRING = "String Interpolation in Java with some Java examples."; String first = "Interpolation"; String second = "Java"; String result = MessageFormat.format("String in with some examples.", first, second); assertEquals(EXPECTED_STRING, result); >

Regarding performance, StringBuilder only appends text to a dynamic buffer; however, MessageFormat parses the given format before appending the data. As a result , StringBuilder outperforms MessageFormat in terms of efficiency.

7. Apache Commons

Finally, we have StringSubstitutor from Apache Commons. In the context of this class, values are substituted for variables included within a String. This class takes a piece of text and replaces all the variables. A variable's default definition is $ . Constructors and set methods can be used to alter the prefix and suffixes. The resolution of variable values typically involves the use of a map. However, we can resolve them by utilizing system attributes or supplying a specialized variable resolver:

@Test public void givenTwoString_thenInterpolateWithStringSubstitutor() < String EXPECTED_STRING = "String Interpolation in Java with some Java examples."; String baseString = "String $in $ with some $ examples."; String first = "Interpolation"; String second = "Java"; Map parameters = new HashMap<>(); parameters.put("first", first); parameters.put("second", second); StringSubstitutor substitutor = new StringSubstitutor(parameters); String result = substitutor.replace(baseString); assertEquals(EXPECTED_STRING, result); >