import java.util.Arrays;
import java.util.Scanner;public class Main {public static void main(String[] args) {// TODO Auto-generated method stubScanner cin = new Scanner(System.in);System.out.println("-1234".matches("-?\\d+")); //可能以-开头以数字结尾的System.out.println("5678".matches("-?\\d+"));System.out.println("+1234".matches("-?\\d+"));System.out.println("+2344".matches("(-|\\+)?\\d+"));//可能以-或者+开头以数字结尾的}
}输出：

true
true
false
true

import java.util.Arrays;
import java.util.Scanner;public class Main {public static String s = "I   am a good student... haha";public static void main(String[] args) {//以空格进行分割，返回一个listSystem.out.println( Arrays.asList(s.split(" ")) );//以非字符进行分割 W表示一个 W+表示后边跟任意个System.out.println( Arrays.asList(s.split("\\W+")));//以以g开头后边跟字符的进行分割System.out.println( Arrays.asList(s.split("g\\w+")));}
}输出：
[I, , , am, a, good, student..., haha]
[I, am, a, good, student, haha]
[I   am a ,  student... haha]

import java.util.Arrays;
import java.util.Scanner;public class Main {public static String s = "I   am a good student... haha good";public static void main(String[] args) {System.out.println(s.replaceFirst("g\\w+", "very good"));System.out.println(s.replaceAll("g\\w+", "very good"));}
}输出：
I   am a very good student... haha good
I   am a very good student... haha very good

import java.util.Arrays;
import java.util.Scanner;  public class Main {  public static void main(String[] args) {  // TODO Auto-generated method stub  Scanner cin = new Scanner(System.in);  int n = cin.nextInt();  String s = null;  for (int i = 0; i < n; ++i) {  s = cin.next();  System.out.println(s.replaceAll("cRazY", "CrAZy").replaceAll("CraZy", "cRAzY"));  }  }  }