/* package whatever; // don't place package name! */
import java.util.*;
import java.lang.*;
import java.io.*;
import java.util.regex.*;
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
{
String str
= "someText\n\nbegin\n .someMethod()\n .doSomething(TOKEN_123)\n .someMethod()\nend\n\nbegin\n .someMethod()\n .doSomething(TOKEN_456)\n .someMethod()\nend\n\nbegin\n .someMethod()\n .doSomething(TOKEN_789)\n .someMethod()\nend\n\nmore Text"; System.
out.
println(str.
replaceFirst("(?s)begin(?:(?!begin).)*TOKEN_456.*?end\\s*",
""));
}
}
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