A few tips when using String or Collection part 1

Tuesday, 23/02/2021

Tram Ho

Hello everyone, today I will share about the tip of checking String null or full space conveniently

I will use the library StringUtils class to download the jar file to import into the library at ( link )

If you use maven project, it’s easier, just import in pom.xml file

&lt;!-- https://mvnrepository.com/artifact/org.apache.commons/commons-lang3 --&gt;
&lt;dependency&gt;
    &lt;groupId&gt;org.apache.commons&lt;/groupId&gt;
    &lt;artifactId&gt;commons-lang3&lt;/artifactId&gt;
    &lt;version&gt;3.7&lt;/version&gt;
&lt;/dependency&gt;

<groupId>org.apache.commons</groupId>

<artifactId>commons-lang3</artifactId>

</dependency>

If you want to check if the String is null / full space / empty, then manually check will be like this

<span class="token keyword">package</span> test <span class="token punctuation">;</span>

<span class="token keyword">import</span> <span class="token namespace">org <span class="token punctuation">.</span> apache <span class="token punctuation">.</span> commons <span class="token punctuation">.</span> lang3</span> <span class="token punctuation">.</span> <span class="token class-name">StringUtils</span> <span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Main</span> <span class="token punctuation">{</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span> <span class="token punctuation">(</span> <span class="token class-name">String</span> <span class="token punctuation">[</span> <span class="token punctuation">]</span> args <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token class-name">String</span> a <span class="token operator">=</span> <span class="token keyword">null</span> <span class="token punctuation">;</span>
        <span class="token class-name">String</span> b <span class="token operator">=</span> <span class="token string">""</span> <span class="token punctuation">;</span>
        <span class="token class-name">String</span> c <span class="token operator">=</span> <span class="token string">"              "</span> <span class="token punctuation">;</span>

        <span class="token class-name">System</span> <span class="token punctuation">.</span> out <span class="token punctuation">.</span> <span class="token function">println</span> <span class="token punctuation">(</span> <span class="token string">"manual result: "</span> <span class="token operator">+</span> <span class="token string">"a: "</span> <span class="token operator">+</span> <span class="token function">validateStringManual</span> <span class="token punctuation">(</span> a <span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" b: "</span> <span class="token operator">+</span> <span class="token function">validateStringManual</span> <span class="token punctuation">(</span> b <span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" c: "</span> <span class="token operator">+</span> <span class="token function">validateStringManual</span> <span class="token punctuation">(</span> c <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>

    <span class="token punctuation">}</span>

    <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token class-name">Boolean</span> <span class="token function">validateStringManual</span> <span class="token punctuation">(</span> <span class="token class-name">String</span> str <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span> <span class="token function">length</span> <span class="token punctuation">(</span> str <span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0</span> <span class="token operator">||</span> <span class="token function">isFullspace</span> <span class="token punctuation">(</span> str <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">return</span> <span class="token boolean">true</span> <span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> <span class="token boolean">false</span> <span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">int</span> <span class="token function">length</span> <span class="token punctuation">(</span> <span class="token class-name">CharSequence</span> cs <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> cs <span class="token operator">==</span> <span class="token keyword">null</span> <span class="token operator">?</span> <span class="token number">0</span> <span class="token operator">:</span> cs <span class="token punctuation">.</span> <span class="token function">length</span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">Boolean</span> <span class="token function">isFullspace</span> <span class="token punctuation">(</span> <span class="token class-name">CharSequence</span> cs <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">int</span> strLen <span class="token operator">=</span> <span class="token function">length</span> <span class="token punctuation">(</span> cs <span class="token punctuation">)</span> <span class="token punctuation">;</span>
        <span class="token keyword">for</span> <span class="token punctuation">(</span> <span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span> <span class="token punctuation">;</span> i <span class="token operator">&lt;</span> strLen <span class="token punctuation">;</span> <span class="token operator">++</span> i <span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">if</span> <span class="token punctuation">(</span> <span class="token operator">!</span> <span class="token class-name">Character</span> <span class="token punctuation">.</span> <span class="token function">isWhitespace</span> <span class="token punctuation">(</span> cs <span class="token punctuation">.</span> <span class="token function">charAt</span> <span class="token punctuation">(</span> i <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
                <span class="token keyword">return</span> <span class="token boolean">false</span> <span class="token punctuation">;</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> <span class="token boolean">true</span> <span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

package test ;

import org . apache . commons . lang3 . StringUtils ;

public class Main {

public static void main ( String [ ] args ) {

String a = null ;

String b = "" ;

String c = " " ;

System . out . println ( "manual result: " + "a: " + validateStringManual ( a ) + " b: " + validateStringManual ( b ) + " c: " + validateStringManual ( c ) ) ;

}

private static Boolean validateStringManual ( String str ) {

if ( length ( str ) == 0 || isFullspace ( str ) ) {

return true ;

}

return false ;

}

public static int length ( CharSequence cs ) {

return cs == null ? 0 : cs . length ( ) ;

}

public static Boolean isFullspace ( CharSequence cs ) {

int strLen = length ( cs ) ;

for ( int i = 0 ; i < strLen ; ++ i ) {

if ( ! Character . isWhitespace ( cs . charAt ( i ) ) ) {

return false ;

}

return true ;

}

Output

manual result: a: true b: true c: true

1 2	manual result: a: true b: true c: true

Very long and messy, right?

Now if we use the library, we just need to do this

<span class="token keyword">package</span> test <span class="token punctuation">;</span>

<span class="token keyword">import</span> <span class="token namespace">org <span class="token punctuation">.</span> apache <span class="token punctuation">.</span> commons <span class="token punctuation">.</span> lang3</span> <span class="token punctuation">.</span> <span class="token class-name">StringUtils</span> <span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Main</span> <span class="token punctuation">{</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span> <span class="token punctuation">(</span> <span class="token class-name">String</span> <span class="token punctuation">[</span> <span class="token punctuation">]</span> args <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token class-name">String</span> a <span class="token operator">=</span> <span class="token keyword">null</span> <span class="token punctuation">;</span>
        <span class="token class-name">String</span> b <span class="token operator">=</span> <span class="token string">""</span> <span class="token punctuation">;</span>
        <span class="token class-name">String</span> c <span class="token operator">=</span> <span class="token string">"              "</span> <span class="token punctuation">;</span>
        
        <span class="token class-name">System</span> <span class="token punctuation">.</span> out <span class="token punctuation">.</span> <span class="token function">println</span> <span class="token punctuation">(</span> <span class="token string">"StringUtils result: "</span> <span class="token operator">+</span> <span class="token string">"a: "</span> <span class="token operator">+</span> <span class="token class-name">StringUtils</span> <span class="token punctuation">.</span> <span class="token function">isBlank</span> <span class="token punctuation">(</span> a <span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" b: "</span> <span class="token operator">+</span> <span class="token class-name">StringUtils</span> <span class="token punctuation">.</span> <span class="token function">isBlank</span> <span class="token punctuation">(</span> a <span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" c: "</span> <span class="token operator">+</span> <span class="token class-name">StringUtils</span> <span class="token punctuation">.</span> <span class="token function">isBlank</span> <span class="token punctuation">(</span> c <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>

    <span class="token punctuation">}</span>
 <span class="token punctuation">}</span>

package test ;

public class Main {

String a = null ;

String b = "" ;

String c = " " ;

System . out . println ( "StringUtils result: " + "a: " + StringUtils . isBlank ( a ) + " b: " + StringUtils . isBlank ( a ) + " c: " + StringUtils . isBlank ( c ) ) ;

}

Output

StringUtils result: a: true b: true c: true

1 2	StringUtils result: a: true b: true c: true

Still the same, very convenient, right?

If you do not want to check the fullspace, use the following method:

<span class="token keyword">package</span> test <span class="token punctuation">;</span>

<span class="token keyword">import</span> <span class="token namespace">org <span class="token punctuation">.</span> apache <span class="token punctuation">.</span> commons <span class="token punctuation">.</span> lang3</span> <span class="token punctuation">.</span> <span class="token class-name">StringUtils</span> <span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Main</span> <span class="token punctuation">{</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span> <span class="token punctuation">(</span> <span class="token class-name">String</span> <span class="token punctuation">[</span> <span class="token punctuation">]</span> args <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token class-name">String</span> a <span class="token operator">=</span> <span class="token keyword">null</span> <span class="token punctuation">;</span>
        <span class="token class-name">String</span> b <span class="token operator">=</span> <span class="token string">""</span> <span class="token punctuation">;</span>
        <span class="token class-name">String</span> c <span class="token operator">=</span> <span class="token string">"              "</span> <span class="token punctuation">;</span>

        <span class="token class-name">System</span> <span class="token punctuation">.</span> out <span class="token punctuation">.</span> <span class="token function">println</span> <span class="token punctuation">(</span> <span class="token string">"StringUtils result: "</span> <span class="token operator">+</span> <span class="token string">"a: "</span> <span class="token operator">+</span> <span class="token class-name">StringUtils</span> <span class="token punctuation">.</span> <span class="token function">isEmpty</span> <span class="token punctuation">(</span> a <span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" b: "</span> <span class="token operator">+</span> <span class="token class-name">StringUtils</span> <span class="token punctuation">.</span> <span class="token function">isEmpty</span> <span class="token punctuation">(</span> a <span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" c: "</span> <span class="token operator">+</span> <span class="token class-name">StringUtils</span> <span class="token punctuation">.</span> <span class="token function">isEmpty</span> <span class="token punctuation">(</span> c <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>

    <span class="token punctuation">}</span>

<span class="token punctuation">}</span>

package test ;

public class Main {

String a = null ;

String b = "" ;

String c = " " ;

System . out . println ( "StringUtils result: " + "a: " + StringUtils . isEmpty ( a ) + " b: " + StringUtils . isEmpty ( a ) + " c: " + StringUtils . isEmpty ( c ) ) ;

}

Output

StringUtils result: a: true b: true c: false

1 2	StringUtils result: a: true b: true c: false

StringUtils has many other libraries that you can check and use for your purposes. For example, isNotBlank (), isNotEmpty () …

Now let’s move on to validate Collections in java

Maven project, then add this paragraph to pom.xml file:

&lt;!-- https://mvnrepository.com/artifact/org.apache.commons/commons-collections4 --&gt;
&lt;dependency&gt;
    &lt;groupId&gt;org.apache.commons&lt;/groupId&gt;
    &lt;artifactId&gt;commons-collections4&lt;/artifactId&gt;
    &lt;version&gt;4.1&lt;/version&gt;
&lt;/dependency&gt;

<groupId>org.apache.commons</groupId>

<artifactId>commons-collections4</artifactId>

</dependency>

And java projects usually import jar file to download at the link

An example of checking whether that Collection is empty or null

<span class="token keyword">package</span> test <span class="token punctuation">;</span>

<span class="token keyword">import</span> <span class="token namespace">org <span class="token punctuation">.</span> apache <span class="token punctuation">.</span> commons <span class="token punctuation">.</span> collections4</span> <span class="token punctuation">.</span> <span class="token class-name">CollectionUtils</span> <span class="token punctuation">;</span>

<span class="token keyword">import</span> <span class="token namespace">java <span class="token punctuation">.</span> util</span> <span class="token punctuation">.</span> <span class="token class-name">ArrayList</span> <span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token namespace">java <span class="token punctuation">.</span> util</span> <span class="token punctuation">.</span> <span class="token class-name">List</span> <span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Main</span> <span class="token punctuation">{</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span> <span class="token punctuation">(</span> <span class="token class-name">String</span> <span class="token punctuation">[</span> <span class="token punctuation">]</span> args <span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token class-name">List</span> <span class="token generics"><span class="token punctuation">&lt;</span> <span class="token class-name">String</span> <span class="token punctuation">&gt;</span></span> list1 <span class="token operator">=</span> <span class="token keyword">null</span> <span class="token punctuation">;</span>
        <span class="token class-name">List</span> <span class="token generics"><span class="token punctuation">&lt;</span> <span class="token class-name">String</span> <span class="token punctuation">&gt;</span></span> list2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span> <span class="token generics"><span class="token punctuation">&lt;</span> <span class="token punctuation">&gt;</span></span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
        <span class="token class-name">List</span> <span class="token generics"><span class="token punctuation">&lt;</span> <span class="token class-name">String</span> <span class="token punctuation">&gt;</span></span> list3 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span> <span class="token generics"><span class="token punctuation">&lt;</span> <span class="token punctuation">&gt;</span></span> <span class="token punctuation">(</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
        list3 <span class="token punctuation">.</span> <span class="token function">add</span> <span class="token punctuation">(</span> <span class="token string">"xxx"</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
        <span class="token class-name">System</span> <span class="token punctuation">.</span> out <span class="token punctuation">.</span> <span class="token function">println</span> <span class="token punctuation">(</span> <span class="token string">"result: "</span> <span class="token operator">+</span> <span class="token string">"list1: "</span> <span class="token operator">+</span> <span class="token class-name">CollectionUtils</span> <span class="token punctuation">.</span> <span class="token function">isEmpty</span> <span class="token punctuation">(</span> list1 <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
        <span class="token class-name">System</span> <span class="token punctuation">.</span> out <span class="token punctuation">.</span> <span class="token function">println</span> <span class="token punctuation">(</span> <span class="token string">"result: "</span> <span class="token operator">+</span> <span class="token string">"list2: "</span> <span class="token operator">+</span> <span class="token class-name">CollectionUtils</span> <span class="token punctuation">.</span> <span class="token function">isEmpty</span> <span class="token punctuation">(</span> list2 <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>
        <span class="token class-name">System</span> <span class="token punctuation">.</span> out <span class="token punctuation">.</span> <span class="token function">println</span> <span class="token punctuation">(</span> <span class="token string">"result: "</span> <span class="token operator">+</span> <span class="token string">"list3: "</span> <span class="token operator">+</span> <span class="token class-name">CollectionUtils</span> <span class="token punctuation">.</span> <span class="token function">isEmpty</span> <span class="token punctuation">(</span> list3 <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">;</span>

    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

package test ;

import org . apache . commons . collections4 . CollectionUtils ;

import java . util . ArrayList ;

import java . util . List ;

public class Main {

List < String > list2 = new ArrayList < > ( ) ;

List < String > list3 = new ArrayList < > ( ) ;

list3 . add ( "xxx" ) ;

}

Output

result: list1: true
result: list2: true
result: list3: false

result: list1: true

result: list2: true

result: list3: false

This is just one of the functions of the CollectionUtils class, depending on the purpose of the use you get to use.

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A few tips when using String or Collection part 1

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