Java-11.4 regular expression (1)-perceptual knowledge

Java-11.4 regular expression (1)-perceptual knowledge

In this section, let's take a look at the regular expression.

A regular expression describes a string in some form.

Note: in java, the backslash of the regular expression must be \. If it is a normal backslash, it must be described.

There are several regular expressions in the string: matches, split, and replaceAll.

1. matches Method

The following is just an example to let everyone feel that the expression is in progress.

 

package com.ray.ch11;public class Test {public static void main(String[] args) {System.out.println(-21.matches(-?\d+));System.out.println(-21.matches(-?\d));System.out.println(+21.matches(\+?\d+));System.out.println(+21.matches((-|\+)?\d+));}}

Output:

 

True
False
True
True

Explanation:

-? Indicates a number with a negative number.

D indicates the integer of each digit.

D + indicates the integer of multiple digits.

| Represents or

\ + Indicates the plus sign. In a regular expression, the plus sign must be preceded by a backslash.

 

2. split Method

Split can accept strings or regular expressions.

 

package com.ray.ch11;import java.util.Arrays;public class Test {public static void main(String[] args) {System.out.println(Arrays.toString(-21a333adg.split(-?\d)));System.out.println(Arrays.toString(-21a333adg.split(\d)));System.out.println(Arrays.toString(-21a333adg.split(\d\d)));System.out.println(Arrays.toString(-21a333adg.split(-\d\d)));System.out.println(Arrays.toString(-21a333adg.split(a)));System.out.println(Arrays.toString(-21a333adg.split(d)));System.out.println(Arrays.toString(-21a333adg.split(g)));}}

Output:

 

[, A, adg]
[-, A, adg]
[-, A, 3adg]
[, A333adg]
[-21,333, dg]
[-21a333a, g]
[-21a333ad]
 

 

 

3. replaceAll Method

ReplaceAll can accept strings or regular expressions.

package com.ray.ch11;public class Test {public static void main(String[] args) {System.out.println(-21a333adg.replaceAll(-?\d, 0));System.out.println(-21a333adg.replaceAll(\d, 0));System.out.println(-21a333adg.replaceAll(\d\d, 0));System.out.println(-21a333adg.replaceAll(-\d\d, 0));System.out.println(-21a333adg.replaceAll(a, 0));System.out.println(-21a333adg.replaceAll(d, 0));System.out.println(-21a333adg.replaceAll(g, 0));}}

Output:

00a000adg
-00a000adg
-0a03adg
0a333adg
-2103330dg
-21a333a0g
-21a333ad0

The first four of the above methods use regular expressions, and the last three are simple strings accepted.

 

Summary: This chapter provides several examples to give you a perceptual knowledge of regular expressions and shows three methods in strings that can accept regular expressions.