javabeginner

Java String Formatting and Templates

String formatting techniques: printf, format, MessageFormat, StringJoiner, and text block interpolation.

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import java.text.MessageFormat;
import java.time.LocalDateTime;
import java.util.*;
import java.util.stream.Collectors;

public class StringFormatting {
    public static void main(String[] args) {

        // 1. String.format / printf
        String name = "Alice";
        int age = 30;
        double balance = 1234.567;

        String formatted = String.format("Name: %-10s Age: %03d Balance: $%,.2f", name, age, balance);
        System.out.println(formatted);
        // Name: Alice      Age: 030 Balance: $1,234.57

        // 2. Date/time formatting
        System.out.printf("Now: %tF %tT%n", LocalDateTime.now(), LocalDateTime.now());

        // 3. MessageFormat (i18n-friendly)
        String msg = MessageFormat.format(
            "Hello {0}, you have {1,number,integer} messages",
            "Bob", 42);
        System.out.println(msg);

        // 4. StringJoiner
        StringJoiner joiner = new StringJoiner(", ", "[", "]");
        joiner.add("apple").add("banana").add("cherry");
        System.out.println(joiner); // [apple, banana, cherry]

        // 5. Collectors.joining
        List<String> fruits = List.of("apple", "banana", "cherry");
        String joined = fruits.stream().collect(Collectors.joining(" | ", "{ ", " }"));
        System.out.println(joined); // { apple | banana | cherry }

        // 6. Text blocks for templates
        String html = """
            <html>
              <body>
                <h1>Hello, %s!</h1>
                <p>Your balance: $%,.2f</p>
              </body>
            </html>
            """.formatted(name, balance);
        System.out.println(html);

        // 7. StringBuilder for dynamic construction
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 5; i++) {
            sb.append("Row ").append(i).append(": ")
              .append("*".repeat(i + 1)).append("\n");
        }
        System.out.print(sb);

        // 8. Repeat and pad
        String padded = "Hello".concat(" ".repeat(15)).substring(0, 20);
        System.out.printf("[%20s]%n", "right-aligned");
        System.out.printf("[%-20s]%n", "left-aligned");
    }
}