What I researched about Java 7

Overview

To upgrade Java knowledge that stopped at "1.4" I am learning about Java7,8,9. This time, I will only describe what I investigated about the functions added in "7".

What I looked up

Diamond operator

You can now omit generics when instantiating.

List<Map<String, List<String>>> gyunyu = new ArrayList<>();

NIO2 A file system related API has been added.

Read file

try {
  Path path = Paths.get("gyunyu.txt");
  List<String> list = Files.readAllLines(path, Charset.forName("UTF-8"));

  for (String gyunyu : list) {
    System.out.println(gyunyu);
  }
} catch(IOException e) {
  e.printStackTrace();
}

Writing a file

try {
  List<String> list = new ArrayList<>();
  list.add("Lemon milk");

  Path path = Paths.get("gyunyu.txt");
  Files.write(path, list, Charset.forName("UTF-8"), StandardOpenOption.APPEND);
} catch (IOException e) {
  e.printStackTrace();
}

• java.nio.file.Path interface. An object that can be used to identify the path of a file or directory

• java.nio.file.Paths Class for creating Path object --Paths.get (URI uri): Converts the specified URI to a Path object

• java.nio.file.Files A class that collects processing related to files or directories --Files.readAllLines (Path path, Charset cs): Read all lines from the file --Files.write (Path path, Iterable <? extends CharSequence> lines, Charset cs, OpenOption ... options) : Write text lines to a file

• java.nio.file.StandardOpenOption Enumeration class that defines how to work with files --StandardOpenOption.APPEND: Write at the end of the file, not at the beginning

try-with-resources By using the try-with-resources statement, you no longer have to write theclose ()that was described in accessing the file database. Preventing memory leaks due to forgetting to write, it has become possible to save a little time and effort.

try(BufferedReader reader = new BufferedReader(new FileReader("gyunyu.txt"))) {
			String line = null;
			while ((line = reader.readLine()) != null) {
				System.out.println(line);
			}
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}

You can use the try-with-resources statement for any class that implements the java.lang.AutoCloseable or java.io.Closeable interface.

Gyunyu.java

public class Gyunyu implements AutoCloseable {
  public void make() {
    System.out.println("coffee");
  }	
  @Override
  public void close() throws Exception {
    System.out.println("milk!!!");
  }
}

try (Gyunyu gyunyu = new Gyunyu()) {
  gyunyu.make();
} catch (Exception e) {
  e.printStackTrace();
}

close () is being executed without calling it like gyunyu.close ().

Catch multiple exceptions

Up to Java 6, I wrote as follows,

try {	
} catch (IllegalArgumentException e) {		
} catch (NullPointerException e) {
}

From Java7, it can be described collectively as follows.

try {
} catch (IllegalArgumentException | NullPointerException e) {
}

Judgment of String in switch statement

You can now use String in switch statements. Up to "1.4", only ʻint can be used, and from "5" to ʻenum can also be used for judgment. From "7", it is now possible to judge by String. I've always thought that it can be judged by String ...

String s = "coffee";
switch (s) {
  case "ichigo":
    System.out.println("ICHIGO GYUNYU !!!");
    break;
  case "coffee":
    System.out.println("COFFEE GYUNYU !!!");
    break;
}