最初にマッチした部分を置換

replaceFirst
public String replaceFirst(String replacement)

String str = "Orange is 100yen, Banana is 180yen.";
String regex = "yen";
Pattern p = Pattern.compile(regex);

Matcher m = p.matcher(str);
String result = m.replaceFirst("YEN");

マッチした部分を全て置換

replaceAll
public String replaceAll(String replacement)

String str = "Orange is 100yen, Banana is 180yen.";
String regex = "yen";
Pattern p = Pattern.compile(regex);

Matcher m = p.matcher(str);
String result = m.replaceAll("YEN");

Stringクラスのメソッド

replaceFirst
public String replaceFirst(String regex, String replacement)

replaceAll
public String replaceAll(String regex, String replacement)

String str = "Orange is 100yen, Banana is 180yen.";
String regex = "yen";

String result = str.replaceAll(regex, "YEN");

サンプルプログラム

/**
 * 指定の文字列に置換
 */
import java.util.regex.Pattern;
import java.util.regex.Matcher;

class JSample1_1{
  public static void main(String args[]){
    String str = "Orange is 100yen, Banana is 180yen.";

    String regex = "yen";
    Pattern p = Pattern.compile(regex);

    Matcher m = p.matcher(str);
    String result1 = m.replaceFirst("YEN");

    System.out.println("replaceFirst");
    System.out.println("before : " + str);
    System.out.println("after  : " + result1);

    String result2 = m.replaceAll("YEN");

    System.out.println("replaceAll");
    System.out.println("before : " + str);
    System.out.println("after  : " + result2);

    String result3 = str.replaceAll(regex, "YEN");

    System.out.println("String.replaceAll");
    System.out.println("before : " + str);
    System.out.println("after  : " + result3);
  }
}

[xxxxxxxx@dddddddddd Replace]$ javac JSample1_1.java
[xxxxxxxx@dddddddddd Replace]$ java JSample1_1
replaceFirst
before : Orange is 100yen, Banana is 180yen.
after  : Orange is 100YEN, Banana is 180yen.
replaceAll
before : Orange is 100yen, Banana is 180yen.
after  : Orange is 100YEN, Banana is 180YEN.
String.replaceAll
before : Orange is 100yen, Banana is 180yen.
after  : Orange is 100YEN, Banana is 180YEN.
[xxxxxxxx@dddddddddd Replace]$ 

String str = "Orange is 100yen, Banana is 180yen.";
String regex = "\\d.+?yen";
Pattern p = Pattern.compile(regex);

Matcher m = p.matcher(str);
String result = m.replaceFirst("_$0_");

String str = "Orange is 100yen, Banana is 180yen.";
String regex = "(\\d.+?)(yen)";
Pattern p = Pattern.compile(regex);

Matcher m = p.matcher(str);
String result = m.replaceFirst("$2_$1");

サンプルプログラム

/**
 * パターン内の括弧毎にマッチした部分文字列を使って置換
 */
import java.util.regex.Pattern;
import java.util.regex.Matcher;

class JSample2_1{
  public static void main(String args[]){
    String str = "Orange is 100yen, Banana is 180yen.";

    String regex = "(\\d.+?)(yen)";
    Pattern p = Pattern.compile(regex);

    Matcher m = p.matcher(str);

    String result1 = m.replaceAll("'$0'");

    System.out.println("replaceAll(\"'$0'\")");
    System.out.println("before : " + str);
    System.out.println("after  : " + result1);

    String result2 = m.replaceAll("$2_$1");

    System.out.println("replaceAll(\"$2_$1\")");
    System.out.println("before : " + str);
    System.out.println("after  : " + result2);

    String result3 = m.replaceAll("\\\\$1");

    System.out.println("replaceAll(\"\\\\$1\")");
    System.out.println("before : " + str);
    System.out.println("after  : " + result3);
  }
}

[xxxxxxxx@dddddddddd Replace]$ javac JSample2_1.java
[xxxxxxxx@dddddddddd Replace]$ java JSample2_1
replaceAll("'$0'")
before : Orange is 100yen, Banana is 180yen.
after  : Orange is '100yen', Banana is '180yen'.
replaceAll("$2_$1")
before : Orange is 100yen, Banana is 180yen.
after  : Orange is yen_100, Banana is yen_180.
replaceAll("\\$1")
before : Orange is 100yen, Banana is 180yen.
after  : Orange is \100, Banana is \180.
[xxxxxxxx@dddddddddd Replace]$ 

String str = "Orange is 100dollar, Banana is 180dollar.";
String regex = "(\\d.+?)dollar";
Pattern p = Pattern.compile(regex);

Matcher m = p.matcher(str);
String result = m.replaceFirst("\\$$1");

tring str = "Orange is 100yen, Banana is 180yen.";
String regex = "(\\d.+?)dollar";
Pattern p = Pattern.compile(regex);

Matcher m = p.matcher(str);
String result = m.replaceFirst("\\\\$1");

サンプルプログラム

/**
 * 置換の時のエスケープ処理
 */
import java.util.regex.Pattern;
import java.util.regex.Matcher;

class JSample3_1{
  public static void main(String args[]){
    String str = "Orange is 100dollar, Banana is 180dollar.";

    String regex = "(\\d.+?)dollar";
    Pattern p = Pattern.compile(regex);

    Matcher m = p.matcher(str);

    String result = m.replaceAll("\\$$1");

    System.out.println("replaceAll(\"\\$$1\")");
    System.out.println("before : " + str);
    System.out.println("after  : " + result);
  }
}

[xxxxxxxx@dddddddddd Replace]$ javac JSample3_1.java
[xxxxxxxx@dddddddddd Replace]$ java JSample3_1
replaceAll("\$$1")
before : Orange is 100dollar, Banana is 180dollar.
after  : Orange is $100, Banana is $180.
[xxxxxxxx@dddddddddd Replace]$