[JAVA] Organize methods that can be used with StringUtils

StringUtils had a lot of methods that I could use, so I've organized the ones that I found useful.

What is StringUtils?

https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html

It is a method that summarizes various convenient operations for string type string editing. Unlike the String method, it takes care not to cause nullpo. No need to check for null. Note that it is similar to StringUtil

isEmpty and isNotEmpty

isEmpty is also a String, but it allows nulls and returns false. isNotEmpty is the opposite of isEmpty.

isEmpty.isNotEmpty


        String a = "1234";
        String b = "";
        String c = null;

        try {
        System.out.println(StringUtils.isEmpty(a));
        System.out.println(StringUtils.isNotEmpty(a));
        System.out.println(a.isEmpty());
        System.out.println(StringUtils.isEmpty(b));
        System.out.println(StringUtils.isNotEmpty(b));
        System.out.println(b.isEmpty());
        System.out.println(StringUtils.isEmpty(c));
        System.out.println(StringUtils.isNotEmpty(c));
        System.out.println(c.isEmpty());
        }catch (Exception e) {
            System.out.println("Nullpo");
        }

result.


false
true
false
true
false
true
true
false
Nullpo

isBlank and isNotBlank

A method that checks for whitespace and null that String does not have. If all the variables are not blank, the blank judgment is not made.

isBlank.isNotBlank


        String a = "1234";
        String b = "12 4";
        String c = " ";
        String d = " ";
        String e = "";
        String f = null;

        System.out.println(StringUtils.isBlank(a));
        System.out.println(StringUtils.isNotBlank(a));
        System.out.println(StringUtils.isBlank(b));
        System.out.println(StringUtils.isNotBlank(b));
        System.out.println(StringUtils.isBlank(c));
        System.out.println(StringUtils.isNotBlank(c));
        System.out.println(StringUtils.isBlank(d));
        System.out.println(StringUtils.isNotBlank(d));
        System.out.println(StringUtils.isBlank(e));
        System.out.println(StringUtils.isNotBlank(e));
        System.out.println(StringUtils.isBlank(f));
        System.out.println(StringUtils.isNotBlank(f));

result.


false
true
false
true
true
false
true
false
true
false
true
false

isAllLowerCase Make sure it is in lowercase only. Whitespace, empty string, null is false

isAllLowerCase.


        String a = "a";
        String b = "A";
        String c = "Aa";
        String d = "Ah";
        String e = "1";
        String f = " ";
        String h = null;

        System.out.println(StringUtils.isAllLowerCase(a));
        System.out.println(StringUtils.isAllLowerCase(b));
        System.out.println(StringUtils.isAllLowerCase(c));
        System.out.println(StringUtils.isAllLowerCase(d));
        System.out.println(StringUtils.isAllLowerCase(e));
        System.out.println(StringUtils.isAllLowerCase(f));
        System.out.println(StringUtils.isAllLowerCase(h));
true
false
false
false
false
false
false

isAllUpperCase Make sure it is in uppercase only. Whitespace, empty string, null is false

isAllUpperCase.


        String a = "a";
        String b = "A";
        String c = "Aa";
        String d = "Ah";
        String e = "1";
        String f = " ";
        String h = null;

        System.out.println(StringUtils.isAllUpperCase(a));
        System.out.println(StringUtils.isAllUpperCase(b));
        System.out.println(StringUtils.isAllUpperCase(c));
        System.out.println(StringUtils.isAllUpperCase(d));
        System.out.println(StringUtils.isAllUpperCase(e));
        System.out.println(StringUtils.isAllUpperCase(f));
        System.out.println(StringUtils.isAllUpperCase(h));

result.


false
true
false
false
false
false
false

isAlpha and isAlphaSpace

isAlpha checks if it is a character. Numbers, spaces, empty strings, null are false isAlphaSpace is a blank-tolerant version of isAlpha

isAlpha.isAlphaSpace


        String a = "a";
        String b = "A";
        String c = "1";
        String d = "1aB";
        String e = "Ah";
        String f = " ";
        String h = null;

        System.out.println(StringUtils.isAlpha(a));
        System.out.println(StringUtils.isAlpha(b));
        System.out.println(StringUtils.isAlpha(c));
        System.out.println(StringUtils.isAlpha(d));
        System.out.println(StringUtils.isAlpha(e));
        System.out.println(StringUtils.isAlpha(f));
        System.out.println(StringUtils.isAlpha(h));

result.


true
true
false
false
true
false
false

isNumeric and isNumericSpace

isNumeric checks if it is a number. Numbers, spaces, empty strings, null are false isNumericSpace is a blank-tolerant version of isNumeric

isNumeric.isNumericSpace


        String a = "a";
        String b = "A";
        String c = "1";
        String d = "1aB";
        String e = "Ah";
        String f = " ";
        String h = null;

        System.out.println(StringUtils.isNumeric(a));
        System.out.println(StringUtils.isNumeric(b));
        System.out.println(StringUtils.isNumeric(c));
        System.out.println(StringUtils.isNumeric(d));
        System.out.println(StringUtils.isNumeric(e));
        System.out.println(StringUtils.isNumeric(f));
        System.out.println(StringUtils.isNumeric(h));

result.


false
false
true
false
false
false
false

isAlphanumeric and isAlphanumericSpace

isAlphanumeric = isAlpha + isNumeric isAlphanumericSpace = isAlphaSpace + isNumericSpace

isAlphanumeric.isAlphanumericSpace


        String a = "a";
        String b = "A";
        String c = "1";
        String d = "1aB";
        String e = "Ah";
        String f = " ";
        String h = null;

        System.out.println(StringUtils.isAlphanumeric(a));
        System.out.println(StringUtils.isAlphanumericSpace(a));
        System.out.println(StringUtils.isAlphanumeric(b));
        System.out.println(StringUtils.isAlphanumericSpace(b));
        System.out.println(StringUtils.isAlphanumeric(c));
        System.out.println(StringUtils.isAlphanumericSpace(c));
        System.out.println(StringUtils.isAlphanumeric(d));
        System.out.println(StringUtils.isAlphanumericSpace(d));
        System.out.println(StringUtils.isAlphanumeric(e));
        System.out.println(StringUtils.isAlphanumericSpace(e));
        System.out.println(StringUtils.isAlphanumeric(f));
        System.out.println(StringUtils.isAlphanumericSpace(f));
        System.out.println(StringUtils.isAlphanumeric(h));
        System.out.println(StringUtils.isAlphanumericSpace(h));

result.


true
true
true
true
true
true
true
true
true
true
false
true
false
false

contains and contains None

Check if the second argument is included in the first argument. Null allowed. containsNone is the opposite of contains

contains.containsNone


        String tar = "abcdef";
        String a = "a";
        String b = "B";
        String c = "abc";
        String d = "abC";
        String e = "";
        String f = null;

        try {
            System.out.println(StringUtils.contains(tar, a));
            System.out.println(StringUtils.containsNone(tar, a));
            System.out.println(tar.contains(a));
            System.out.println(StringUtils.contains(tar, b));
            System.out.println(StringUtils.containsNone(tar, b));
            System.out.println(tar.contains(b));
            System.out.println(StringUtils.contains(tar, c));
            System.out.println(StringUtils.containsNone(tar, c));
            System.out.println(tar.contains(c));
            System.out.println(StringUtils.contains(tar, d));
            System.out.println(StringUtils.containsNone(tar, d));
            System.out.println(tar.contains(d));
            System.out.println(StringUtils.contains(tar, e));
            System.out.println(StringUtils.containsNone(tar, e));
            System.out.println(tar.contains(e));
            System.out.println(StringUtils.contains(tar, f));
            System.out.println(StringUtils.containsNone(tar, f));
            System.out.println(tar.contains(f));
        } catch (Exception ex) {
            System.out.println("Nullpo");
        }
true
false
true
false
true
false
true
false
true
false
false
false
true
true
true
false
true
Nullpo

equals A null-checked version of the String equals method. Either can be used as null. However, even if both are null, it will be false.

equals.


        String a = "a";
        String b = "abc";
        String c = " ";
        String d = "";
        String e = null;
        
        try {
            System.out.println(StringUtils.equals(a, a));
            System.out.println(a.equals(a));
            System.out.println(StringUtils.equals(a, b));
            System.out.println(a.equals(b));
            System.out.println(StringUtils.equals(a, c));
            System.out.println(a.equals(c));
            System.out.println(StringUtils.equals(a, d));
            System.out.println(a.equals(d));
            System.out.println(StringUtils.equals(a, e));
            System.out.println(a.equals(e));
            System.out.println(StringUtils.equals(c, c));
            System.out.println(c.equals(c));
            System.out.println(StringUtils.equals(c, d));
            System.out.println(c.equals(d));
            System.out.println(StringUtils.equals(d, d));
            System.out.println(d.equals(d));
            System.out.println(StringUtils.equals(d, e));
            System.out.println(e.equals(e));
            System.out.println(StringUtils.equals(e, e));
            System.out.println(StringUtils.equals(e, a));
            System.out.println(e.equals(e));
        } catch (Exception ex) {
            System.out.println("Nullpo");
        }

result.


true
true
false
false
false
false
false
false
false
false
true
true
false
false
true
true
false
Nullpo

join It arranges a list of character strings separated by (comma) to make one character string. The join of the String object will be dropped by nullpo if the list object is null.

join.


        List<String> strList = new ArrayList<>();
        List<String> nullList = null;
        try {
            for (int i = 0; i < 10; i++) {
                strList.add(Integer.toString(i));
            }
            strList.add(" ");
            strList.add("");
            strList.add(null);

            System.out.println(StringUtils.join(strList));
            System.out.println(StringUtils.join(nullList));
            System.out.println(String.join(",", nullList));
        } catch (Exception e) {
            System.out.println("Nullpo");
        }
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9,  , , null]

Nullpo

leftPad、rightPad It fills the left and right sides of the character string with spaces so that the specified number of characters is reached. You can also specify the characters to fill in instead of the blank plum.

leftPad.rightPad


        String a = "a";
        System.out.println(StringUtils.leftPad(a, 5));
        System.out.println(StringUtils.leftPad(a, 5, "0"));
        System.out.println(StringUtils.rightPad(a, 5));
        System.out.println(StringUtils.rightPad(a, 5, "0"));

result.


    a
0000a
a    
a0000

repeat It creates a character string that repeats the specified character string a specified number of times. If it is null, it will not be repeated.

repeat.


        String a = "abc";
        String b = " ";
        String c = "";
        String d = null;
        System.out.println(StringUtils.repeat(a, 5));
        System.out.println(StringUtils.repeat(b, 5));
        System.out.println(StringUtils.repeat(c, 5));
        System.out.println(StringUtils.repeat(d, 5));

result.


abcabcabcabcabc
     

null

swapCase Automatically convert uppercase letters to lowercase letters and lowercase letters to uppercase letters!

swapCase.


        String a = "abcdefgh";
        String b = "ABCDEFGH";
        String c = "aBcDeFgH";
        System.out.println(StringUtils.swapCase(a));
        System.out.println(StringUtils.swapCase(b));
        System.out.println(StringUtils.swapCase(c));

result.


ABCDEFGH
abcdefgh
AbCdEfGh

defaultString If the target character string is null, it will be changed to an empty string. Useful when you don't want to display null.

defaultString.


        String a = "abc";
        String b = " ";
        String c = "";
        String d = null;
        System.out.println(StringUtils.defaultString(a));
        System.out.println(StringUtils.defaultString(b));
        System.out.println(StringUtils.defaultString(c));
        System.out.println(StringUtils.defaultString(d));

result.


abc
    


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