[JAVA] Road to REPL (?) Creation (2)

Introduction

This is the second time to create REPL for Java 8. Please refer to the first article for the purpose and precautions.

• Road to REPL (?) Creation (1)

Now let's get into the source description.

Console interface

An interface that provides access to the Windows cmd and the Eclipse console.

• ```input ()` `` Interface to accept input from the console.
• ``` Print ()` `` Interface of screen output method.
• ``` Cleanup () Interface.Finalizable Interface to the methods of the interface.
  Interface.Finalizeable The interface will be explained later.

interface Interface { ... }It is not a mistake, but a dummy interface.

 If you create a small interface as a single file, the file system becomes complicated, so we will add the interface in this.


#### **`Interface.java`**
```java

package console;

interface Interface {
    /** console interface. */
    interface Console extends Interface.Finalizable {
        // methods for input string from console ======================================
        default String input(String prompt);

        // methods for output string to console =======================================
        void print(String format, Object... args);
        void print(String s);

        // extends Inteeface.Finalizeable =============================================
        void cleanup();
    }
    // ... more interface ...
}

Console service

This file is also packed ... The concrete console class is simply created and passed by `Console.create ()`.

Service.java

package console;

public interface Service {
    class Console {
        public  static final String newLine = System.lineSeparator();
        private static final String defaultEncoding = "UTF-8";

        public  static Interface.Console create(String encoding) {
            if ( encoding == null  ||  encoding.trim().isEmpty() ) { 
                encoding = defaultEncoding; 
            }
            if ( !java.nio.charset.Charset.isSupported(encoding) ) {
                encoding = defaultEncoding; 
            }
            return    (System.console() != null)
                    ? new SystemConsole(System.console())
                    : new StandardConsole(encoding);
        }

        // ///////////////////////////////////////////////////////////////////////////////
        /** console uses standard in/out class.
         */ // ///////////////////////////////////////////////////////////////////////////
        private static class StandardConsole implements Interface.Console {
            protected StandardConsole(String encoding) {
                try {
                    java.io.InputStreamReader istream = new java.io.InputStreamReader(System.in, encoding);
                    reader_  = new java.io.BufferedReader(istream);
                    out_     = new java.io.PrintStream(System.out, true, encoding);
                } catch (java.io.IOException e) {
                    System.out.println( e.getMessage() );
                }
            }

            // methods for input string from console ===============================
            public String input(String prompt) {
                out_.printf(prompt);
                String s = "";
                try {
                    s = reader_.readLine();
                } catch (java.io.IOException e) {
                    System.out.println( e.getMEssage() );
                }
                return s;
            }

            // methods for output string to console ================================
            public void print(String format, Object... args) { out_.printf(format, args); }
            public void print(String s)                      { out_.println(s);           }

            // implements Finalizable.cleanup() ====================================
            public void cleanup() {
                out_.close();
                out_ = null;
                try {
                    reader_.close();
                    reader_ = null;
                } catch(java.io.IOException e) {
                    System.out.println( e.getMessage() );
                }
            }

            // internal fields =====================================================
            java.io.BufferedReader reader_;
            java.io.PrintStream    out_;
        }

        // ///////////////////////////////////////////////////////////////////////////////
        /** console uses System.console() class.
         */ // ///////////////////////////////////////////////////////////////////////////
        private static class SystemConsole implements Interface.Console {
            protected SystemConsole(java.io.Console con) {
                console_ = con;
            }

            // methods for input string from console ===============================
            public String input(String prompt) { return console_.readLine(prompt); }

            // methods for output string to console ================================
            public void print(String format, Object... args) {
               console_.printf(format, args); 
            }
            public void print(String s) {
                console_.printf(s + Service.Console.newLine); 
            }

            // implements Finalizable.cleanup() ====================================
            public void cleanup() { /* no operation */ }

            // internal fields =====================================================
            java.io.Console console_;
        }
    }
}

Description

Service.Console Although it says service, it's actually a factory class in Console. It takes the console encoding name and creates and returns a concrete console class based on it. If an incorrect encoding name is passed, the default "UTF-8" will be set.

• If ``` System.console ()` `` (java 1.6 or later) is available, it returns a console object (SystemConsole) that uses it.
• If ``` System.console ()` `` is not available, returns a console object (StandardinConsole) with standard I / O (InputStreamReader and PrintStream).
  When used as a normal application, the standard input / output console is not used, but System.console cannot be used in the console window used when executing with Eclipse or IntelliJ, so this is used. I will.

python

public interface Service {
    class Console {
        public  static final String newLine = System.lineSeparator();
        private static final String defaultEncoding = "UTF-8";

        public  static Interface.Console create(String encoding) {
            if ( encoding == null  ||  encoding.trim().isEmpty() ) { 
                encoding = defaultEncoding; 
            }
            if ( !java.nio.charset.Charset.isSupported(encoding) ) {
                encoding = defaultEncoding; 
            }
            return    (System.console() != null)
                    ? new SystemConsole(System.console())
                    : new StandardConsole(encoding);
        }
        // ... inner class ...
}

SystemConsole This is a console class that uses System.Console. I don't think any explanation is necessary because the processing is simply delegated. In the above Service.Console, I am trying hard to check the encoding, but here I will not use it because the encoding actually used in the console (cmd.exe etc.) is initialized ( Apparently, there seems to be no way to change it).

python

public interface Service {
    class Console {
        // ...abridgement...

        // ///////////////////////////////////////////////////////////////////////////////
        /** console uses System.console() class.
         */ // ///////////////////////////////////////////////////////////////////////////
        private static class SystemConsole implements Interface.Console {
            protected SystemConsole(java.io.Console con) { console_ = con; }

            // methods for input string from console ===============================
            public String input(String prompt) { return console_.readLine(prompt); }

            // methods for output string to console ================================
            public void print(String format, Object... args) {
               console_.printf(format, args); 
            }
            public void print(String s) {
                console_.printf(s + Service.Console.newLine); 
            }

            // implements Finalizable.cleanup() ====================================
            public void cleanup() { /* no operation */ }

            // internal fields =====================================================
            java.io.Console console_;
        }
    }
}

StandardinConsole This is a console class that uses standard I / O. It's just doing the same thing as the System Console, but thanks to the boilerplate it doubles the amount of code. Even so, the amount of description is reduced because the encoding check is performed at the factory.

• ``` StandardConsole (String)` `` The encoding name received by the argument is set in BufferReader and PrintStream.
• It should just display the input (String) `` `prompt and return the string received from BufferdReader.readLine () `` `, but the code that should only take two lines is awkward Especially ... ~~ This kind of place is annoying and disgusting ~~
• ``` print ()` `` This is just transferring to PrintStream.
• ``` Cleanup ()` `` Interface.Finalizable is an implementation of the interface method. Even though BufferdReader and PrintStream are doing the same processing, only one needs exception checking ... Such a place (ry

python

public interface Service {
    class Console {
        // ...abridgement...

        // ///////////////////////////////////////////////////////////////////////////////
        /** console uses standard in/out class.
         */ // ///////////////////////////////////////////////////////////////////////////
        private static class StandardConsole implements Interface.Console {
            protected StandardConsole(String encoding) {
                try {
                    java.io.InputStreamReader istream = new java.io.InputStreamReader(System.in, encoding);
                    reader_  = new java.io.BufferedReader(istream);
                    out_     = new java.io.PrintStream(System.out, true, encoding);
                } catch (java.io.IOException e) {
                    System.out.println( e.getMessage() );
                }
            }

            // methods for input string from console ===============================
            public String input(String prompt) {
                out_.printf(prompt);
                String s = "";
                try {
                    s = reader_.readLine();
                } catch (java.io.IOException e) {
                    System.out.println( e.getMessage() );
                }
                return s;
            }

            // methods for output string to console ================================
            public void print(String format, Object... args) { out_.printf(format, args); }
            public void print(String s)                      { out_.println(s);           }

            // implements Finalizable.cleanup() ====================================
            public void cleanup() {
                out_.close();
                out_ = null;
                try {
                    reader_.close();
                    reader_ = null;
                } catch(java.io.IOException e) {
                    System.out.println( e.getMessage() );
                }
            }

            // internal fields =====================================================
            java.io.BufferedReader    reader_;
            java.io.PrintStream       out_;
    }
}

BaseREPL fix

The previous BaseREPL is also modified because you need to pass the encoding name. Here, only the corrected parts are described. See Previous article for the full code.

• The `BaseREPL ()` constructor now receives the encoding name to pass to the console.
  In the original plan, it was supposed to pass the console object statically generated by Service.Console, but since it was changed to instantiate and pass, the initialization is moved to the constructor. ..

BaseREPL.java

class BaseREPL {
    BaseREPL(String encoding) {
        if ( encoding == null  ||  encoding.trim().isEmpty() ) { encoding = "UTF-8"; }
        console_ = Service.Console.create(encoding);
    }
    // ...Omitted on the way...
    // internal fields =============================================================
    protected final Interface.Console console_;
}

Summary

This time, I explained the console used by REPL. Initially it was compact, but while I was fixing it, it became a decent volume.

A few more times, we'll continue to create classes to include in the REPL.