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readString and writeString

Learn text I/O with Files.readString and writeString.

readString and writeString

In Java 11+, Files.writeString(path, text) writes text to a file; Files.readString(path) reads all text in one go. This is ideal for small and medium files.

Path p = Files.createTempFile("d", ".txt");
Files.writeString(p, "Hello");
String s = Files.readString(p);
// s equals "Hello"

This is much shorter than the old BufferedReader chain. UTF-8 is the default encoding; for a different encoding, call with StandardCharsets. For large files, mind the memory consumption.

Specifying encoding

The default encoding is UTF-8. If a different encoding is needed, specify it as Files.readString(p, StandardCharsets.ISO_8859_1).

import java.nio.charset.StandardCharsets;

String s = Files.readString(p, StandardCharsets.UTF_8);

UTF-8 is safe for files with Turkish characters. Wrong encoding makes characters look broken. This is a common source of bugs in international applications; be careful.

Practice Write and read text

Write main in a StringDemo class; create a temp file with Files.createTempFile("d", ".txt"). Write text with Files.writeString(p, "Hello"). Read it back with String s = Files.readString(p). Print with System.out.println(s).

Starter code

Main.java
import java.nio.file.*;

// Write main in StringDemo

// Create temp file; write with writeString; read with readString; print

Sample solution

Main.java
import java.nio.file.*;

class StringDemo {
    public static void main(String[] args) throws Exception {
        Path p = Files.createTempFile("d", ".txt");
        Files.writeString(p, "Hello");
        String s = Files.readString(p);
        System.out.println(s);
    }
}

Expected output

Hello

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Match readString/writeString concepts

Term Meaning
writeString Writes text to a file
readString Reads all text
createTempFile Creates a temp file
Files.exists Checks existence

2 Complete the readString call

Question 
Path p = Files.createTempFile("d", ".txt");
Files.writeString(p, "Merhaba");
String s = Files.____(p);
Answer 
Path p = Files.createTempFile("d", ".txt");
Files.writeString(p, "Merhaba");
String s = Files.readString(p);

Explanation: readString reads all text in one go.

3 In which version was Files.readString added?

  • Java 11 Correct answer
  • Java 8
  • Java 9
  • Java 10

Explanation: readString was added in Java 11.

All lessons in Advanced

1 Advanced stream

  1. collect groupingBy
  2. partitioningBy
  3. joining
  4. reduce
  5. flatMap
  6. Summary - Advanced stream

2 Optional

  1. Optional.of
  2. ofNullable
  3. map and flatMap
  4. orElse and orElseGet
  5. ifPresent and isPresent
  6. Summary - Optional

3 Functional interface

  1. Function<T,R>
  2. Predicate<T>
  3. Consumer<T>
  4. Supplier<T>
  5. @FunctionalInterface
  6. Summary - Functional interface

4 Date/time API

  1. LocalDate
  2. LocalTime and LocalDateTime
  3. Duration and Period
  4. DateTimeFormatter
  5. Instant and ZonedDateTime
  6. Summary - Date/time API

5 Reflection

  1. Class<?>
  2. getFields
  3. getMethods
  4. invoke
  5. getDeclaredConstructors
  6. Summary - Reflection

6 Annotation

  1. Built-in annotations
  2. @interface
  3. Retention and Target
  4. Annotation values
  5. Annotations via reflection
  6. Summary - Annotation

7 Design patterns

  1. Singleton
  2. Factory
  3. Strategy
  4. Observer
  5. Decorator
  6. Summary - Design patterns

8 JUnit test

  1. JUnit basics
  2. Assertions
  3. @BeforeEach and @AfterEach
  4. @ParameterizedTest
  5. @DisplayName
  6. Summary - JUnit test

9 Mockito

  1. Mock
  2. @Mock
  3. when thenReturn
  4. verify
  5. ArgumentMatchers
  6. Summary - Mockito

10 Multithreading

  1. Thread
  2. Runnable
  3. start and join
  4. synchronized
  5. wait and notify
  6. Summary - Multithreading

11 Concurrent API

  1. ExecutorService
  2. Callable and Future
  3. CompletableFuture
  4. ConcurrentHashMap
  5. Lock and Condition
  6. Summary - Concurrent API

12 I/O and NIO basics

  1. Path
  2. Files
  3. readString and writeString
  4. Buffered I/O
  5. Channels
  6. Summary - I/O and NIO basics

13 Advanced project

  1. Project design
  2. Stream layer
  3. Concurrent layer
  4. Test layer
  5. Putting it together

14 Advanced final

  1. Project design
  2. Stream layer
  3. Concurrent layer
  4. Reflection and annotation
  5. Putting it together