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Below is Lexer.java, Token.java, StringHandler.java, and Main.java. I need help in writing test cases. Please write unit tests for lexer.java and make sure to show the full code with the screenshot of the output. Make sure to include the test cases as well.  Lexer.java import java.util.LinkedList;   public class Lexer { private StringHandler stringHandler;     private int lineNumber;     private int charPosition;              public Lexer(String input) {         stringHandler = new StringHandler(input);         lineNumber = 1;         charPosition = 0;     }       public LinkedList lex() {         LinkedList tokens = new LinkedList<>();                        while (!stringHandler.isDone()) {             char c = stringHandler.peek(0);               if (c == ' ' || c == '\t') {                 stringHandler.swallow(1);                 charPosition++;             } else if (c == '\n') {                 tokens.add(new Token(TokenType.SEPARATOR, lineNumber, charPosition));                 stringHandler.swallow(1);                 lineNumber++;                 charPosition = 0;                             } else if (Character.isLetter(c)) {                 tokens.add(processWord());             } else if (Character.isDigit(c)) {                 tokens.add(processNumber());             } else {                 throw new RuntimeException("Unrecognized character: " + c);             }         }           return tokens;     }       private Token processWord() {         StringBuilder value = new StringBuilder();         while (!stringHandler.isDone() && (Character.isLetterOrDigit(stringHandler.peek(0)) || stringHandler.peek(0) == '_' || stringHandler.peek(0) == ',')) {             value.append(stringHandler.getChar());             charPosition++;         }         return new Token(TokenType.WORD, value.toString(), lineNumber, charPosition - value.length());     }           private Token processNumber() {         StringBuilder value = new StringBuilder();         while (!stringHandler.isDone() && (Character.isDigit(stringHandler.peek(0)) || stringHandler.peek(0) == '.')) {             value.append(stringHandler.getChar());             charPosition++;         }         return new Token(TokenType.NUMBER, value.toString(), lineNumber, charPosition - value.length());     } }   Token.java   enum TokenType {     WORD, NUMBER, SEPARATOR } public class Token { private TokenType type;     private String value;     private int lineNumber;     private int charPosition;         public Token(TokenType type, int lineNumber, int charPosition) {         this.type = type;         this.lineNumber = lineNumber;         this.charPosition = charPosition;     }         public Token(TokenType type, String value, int lineNumber, int charPosition) {         this(type, lineNumber, charPosition);         this.value = value;     }       public String toString() {         if (value == null) {             return type.toString();         } else {             return type.toString() + "(" + value + ")";         }     } }         Main.java   import java.io.IOException; import java.nio.file.Files; import java.nio.file.Paths; import java.util.LinkedList;   public class Main {   public static void main(String[] args) {         if (args.length != 1) {             System.out.println("Usage: java Main ");             return;         }               try {             String content = new String(Files.readAllBytes(Paths.get(args[0])));             Lexer lexer = new Lexer(content);             LinkedList tokens = lexer.lex();               for (Token token : tokens) {                 System.out.println(token);             }         } catch (IOException e) {             e.printStackTrace();         }     } }     StringHandler.java   public class StringHandler {     private String document;     private int index;            public StringHandler(String document) {         this.document = document;         this.index = 0;     }         public char peek(int i) {         return document.charAt(index + i);     }       public String peekString(int i) {         return document.substring(index, index + i);     }            public char getChar() {         char c = document.charAt(index);         index++;         return c;     }         public void swallow(int i) {         index += i;     }         public boolean isDone() {         return index >= document.length();     }         public String remainder() {         return document.substring(index);     }

Below is Lexer.java, Token.java, StringHandler.java, and Main.java. I need help in writing test cases. Please write unit tests for lexer.java and make sure to show the full code with the screenshot of the output. Make sure to include the test cases as well.  Lexer.java import java.util.LinkedList;   public class Lexer { private StringHandler stringHandler;     private int lineNumber;     private int charPosition;              public Lexer(String input) {         stringHandler = new StringHandler(input);         lineNumber = 1;         charPosition = 0;     }       public LinkedList lex() {         LinkedList tokens = new LinkedList<>();                        while (!stringHandler.isDone()) {             char c = stringHandler.peek(0);               if (c == ' ' || c == '\t') {                 stringHandler.swallow(1);                 charPosition++;             } else if (c == '\n') {                 tokens.add(new Token(TokenType.SEPARATOR, lineNumber, charPosition));                 stringHandler.swallow(1);                 lineNumber++;                 charPosition = 0;                             } else if (Character.isLetter(c)) {                 tokens.add(processWord());             } else if (Character.isDigit(c)) {                 tokens.add(processNumber());             } else {                 throw new RuntimeException("Unrecognized character: " + c);             }         }           return tokens;     }       private Token processWord() {         StringBuilder value = new StringBuilder();         while (!stringHandler.isDone() && (Character.isLetterOrDigit(stringHandler.peek(0)) || stringHandler.peek(0) == '_' || stringHandler.peek(0) == ',')) {             value.append(stringHandler.getChar());             charPosition++;         }         return new Token(TokenType.WORD, value.toString(), lineNumber, charPosition - value.length());     }           private Token processNumber() {         StringBuilder value = new StringBuilder();         while (!stringHandler.isDone() && (Character.isDigit(stringHandler.peek(0)) || stringHandler.peek(0) == '.')) {             value.append(stringHandler.getChar());             charPosition++;         }         return new Token(TokenType.NUMBER, value.toString(), lineNumber, charPosition - value.length());     } }   Token.java   enum TokenType {     WORD, NUMBER, SEPARATOR } public class Token { private TokenType type;     private String value;     private int lineNumber;     private int charPosition;         public Token(TokenType type, int lineNumber, int charPosition) {         this.type = type;         this.lineNumber = lineNumber;         this.charPosition = charPosition;     }         public Token(TokenType type, String value, int lineNumber, int charPosition) {         this(type, lineNumber, charPosition);         this.value = value;     }       public String toString() {         if (value == null) {             return type.toString();         } else {             return type.toString() + "(" + value + ")";         }     } }         Main.java   import java.io.IOException; import java.nio.file.Files; import java.nio.file.Paths; import java.util.LinkedList;   public class Main {   public static void main(String[] args) {         if (args.length != 1) {             System.out.println("Usage: java Main ");             return;         }               try {             String content = new String(Files.readAllBytes(Paths.get(args[0])));             Lexer lexer = new Lexer(content);             LinkedList tokens = lexer.lex();               for (Token token : tokens) {                 System.out.println(token);             }         } catch (IOException e) {             e.printStackTrace();         }     } }     StringHandler.java   public class StringHandler {     private String document;     private int index;            public StringHandler(String document) {         this.document = document;         this.index = 0;     }         public char peek(int i) {         return document.charAt(index + i);     }       public String peekString(int i) {         return document.substring(index, index + i);     }            public char getChar() {         char c = document.charAt(index);         index++;         return c;     }         public void swallow(int i) {         index += i;     }         public boolean isDone() {         return index >= document.length();     }         public String remainder() {         return document.substring(index);     }

Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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Below is Lexer.java, Token.java, StringHandler.java, and Main.java. I need help in writing test cases. Please write unit tests for lexer.java and make sure to show the full code with the screenshot of the output. Make sure to include the test cases as well. 

Lexer.java

import java.util.LinkedList;
 
public class Lexer {
private StringHandler stringHandler;
    private int lineNumber;
    private int charPosition;
    
 
 
    public Lexer(String input) {
        stringHandler = new StringHandler(input);
        lineNumber = 1;
        charPosition = 0;
    }
 
    public LinkedList<Token> lex() {
        LinkedList<Token> tokens = new LinkedList<>();
        
     
        while (!stringHandler.isDone()) {
            char c = stringHandler.peek(0);
 
            if (c == ' ' || c == '\t') {
                stringHandler.swallow(1);
                charPosition++;
            } else if (c == '\n') {
                tokens.add(new Token(TokenType.SEPARATOR, lineNumber, charPosition));
                stringHandler.swallow(1);
                lineNumber++;
                charPosition = 0;
               
            } else if (Character.isLetter(c)) {
                tokens.add(processWord());
            } else if (Character.isDigit(c)) {
                tokens.add(processNumber());
            } else {
                throw new RuntimeException("Unrecognized character: " + c);
            }
        }
 
        return tokens;
    }
 
    private Token processWord() {
        StringBuilder value = new StringBuilder();
        while (!stringHandler.isDone() && (Character.isLetterOrDigit(stringHandler.peek(0)) || stringHandler.peek(0) == '_' || stringHandler.peek(0) == ',')) {
            value.append(stringHandler.getChar());
            charPosition++;
        }
        return new Token(TokenType.WORD, value.toString(), lineNumber, charPosition - value.length());
    }
 
   
    private Token processNumber() {
        StringBuilder value = new StringBuilder();
        while (!stringHandler.isDone() && (Character.isDigit(stringHandler.peek(0)) || stringHandler.peek(0) == '.')) {
            value.append(stringHandler.getChar());
            charPosition++;
        }
        return new Token(TokenType.NUMBER, value.toString(), lineNumber, charPosition - value.length());
    }
}
 
Token.java
 
enum TokenType {
    WORD, NUMBER, SEPARATOR
}
public class Token {
private TokenType type;
    private String value;
    private int lineNumber;
    private int charPosition;
 
 
    public Token(TokenType type, int lineNumber, int charPosition) {
        this.type = type;
        this.lineNumber = lineNumber;
        this.charPosition = charPosition;
    }
 
 
    public Token(TokenType type, String value, int lineNumber, int charPosition) {
        this(type, lineNumber, charPosition);
        this.value = value;
    }
 
    public String toString() {
        if (value == null) {
            return type.toString();
        } else {
            return type.toString() + "(" + value + ")";
        }
    }
}
 
 
 
 
Main.java
 
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.LinkedList;
 
public class Main {
 
public static void main(String[] args) {
        if (args.length != 1) {
            System.out.println("Usage: java Main <filename>");
            return;
        }
 
   
        try {
            String content = new String(Files.readAllBytes(Paths.get(args[0])));
            Lexer lexer = new Lexer(content);
            LinkedList<Token> tokens = lexer.lex();
 
            for (Token token : tokens) {
                System.out.println(token);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
 
 
StringHandler.java
 
public class StringHandler {
 
 
private String document;
    private int index;
    
 
    public StringHandler(String document) {
        this.document = document;
        this.index = 0;
    }
 
 
    public char peek(int i) {
        return document.charAt(index + i);
    }
 
    public String peekString(int i) {
        return document.substring(index, index + i);
    }
    
 
    public char getChar() {
        char c = document.charAt(index);
        index++;
        return c;
    }
 
 
    public void swallow(int i) {
        index += i;
    }
 
 
    public boolean isDone() {
        return index >= document.length();
    }
 
 
    public String remainder() {
        return document.substring(index);
    }
 
 
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