Java文字列replace（）、replaceFirst（）、replaceAll（）メソッド

replace（）メソッド

replace（） Stringクラスのメソッドは2つの文字列値を受け入れます-

• 置き換えられる文字列（部分文字列）の部分を表すもの。

• 指定された部分文字列を置き換える必要がある文字列を表す別の文字列。

このメソッドを使用すると、Javaで文字列の一部を置き換えることができます。

例

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class ReplaceExample {
   public static void main(String args[]) throws FileNotFoundException {
      String filePath = "D://input.txt";
      Scanner sc = new Scanner(new File(filePath));
      StringBuffer sb = new StringBuffer();
      String input;
      while (sc.hasNextLine()) {
         input = sc.nextLine();
         sb.append(input);
      }
      String contents = sb.toString();
      System.out.println("Contents of the file: \n"+contents);
      System.out.println(" ");
      //Replacing the word with desired one
      contents = contents.replace("Tutorialspoint", "TP");
      System.out.println("Contents of the file after replacing the desired word: \n"+contents);
   }
}

出力

Contents of the file:
Hello how are you welcome to Tutorialspoint. At Tutorialspoint provide hundreds of technical tutorials for free.

Contents of the file after replacing the desired word:
Hello how are you welcome to TP. At TP provide hundreds of technical tutorials for free.

このメソッドの別の変形も、既存の文字と1つの文字をそれぞれ（同じ順序で）表す2つの文字を受け入れ、文字列全体で古い文字を新しい文字に置き換えます。

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class ReplaceExample {
   public static void main(String args[]) throws FileNotFoundException {
      String filePath = "D://input.txt";
      Scanner sc = new Scanner(new File(filePath));
      StringBuffer sb = new StringBuffer();
      String input;
      while (sc.hasNextLine()) {
         input = sc.nextLine();
         sb.append(input);
      }
      String contents = sb.toString();
      System.out.println("Contents of the file: \n"+contents);
      System.out.println(" ");
      //Replacing the word with desired one
      contents = contents.replace('T', '#');
      System.out.println("Contents of the file after replacing the desired word: \n"+contents);
   }
}

出力

Contents of the file:
Hello how are you welcome to Tutorialspoint. At Tutorialspoint provide hundreds of technical tutorials for free.

Contents of the file after replacing the desired word:
Hello how are you welcome to #utorialspoint. At #utorialspoint provide hundreds of technical tutorials for free.

replaceAll（）メソッド

replaceAll（） Stringクラスのメソッドは、正規表現を表す2つの文字列と、置換パターン/文字列を受け入れ、一致した値を指定されたパターン/文字列に置換します。

例

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class replaceAllExample {
   public static void main(String args[]) throws FileNotFoundException {
      String filePath = "D://input.txt";
      Scanner sc = new Scanner(new File(filePath));
      StringBuffer sb = new StringBuffer();
      String input;
      while (sc.hasNextLine()) {
         input = sc.nextLine();
         sb.append(input);
      }
      String contents = sb.toString();
      System.out.println("Contents of the file: \n"+contents);
      System.out.println();
      //Replacing the word with desired one
      contents = contents.replaceAll("\\bTutorialspoint\\b", "TP");
      System.out.println("Contents of the file after replacing the desired word: \n"+contents);
   }
}

出力

Contents of the file:
Hello how are you welcome to Tutorialspoint. At Tutorialspoint provide hundreds of technical tutorials for free.

Contents of the file after replacing the desired word:
Hello how are you welcome to TP. At TP provide hundreds of technical tutorials for free.

replaceFirst（）メソッド

replaceFirst（） Stringクラスのメソッド（また）replaceFirstは、正規表現と置換文字列を表す2つの文字列を受け入れ、最初の一致を置換文字列に置き換えます。

例

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class ReplaceExample {
   public static void main(String args[]) throws FileNotFoundException {
      String filePath = "D://input.txt";
      Scanner sc = new Scanner(new File(filePath));
      StringBuffer sb = new StringBuffer();
      String input;
      while (sc.hasNextLine()) {
         input = sc.nextLine();
         sb.append(input);
      }
      String contents = sb.toString();
      System.out.println("Contents of the file: \n"+contents);
      System.out.println(" ");
      //Replacing the word with desired one
      contents = contents.replaceFirst("Tutorialspoint", "TP");
      System.out.println("Contents of the file after replacing the desired word: \n"+contents);
   }
}

出力

Contents of the file:
Hello how are you welcome to Tutorialspoint. At Tutorialspoint provide hundreds of technical tutorials for free.

Contents of the file after replacing the desired word:
Hello how are you welcome to TP. At Tutorialspoint provide hundreds of technical tutorials for free.

注 −これらの方法はすべて大文字と小文字を区別します。