Why cmd give error when we open uiautomatorviewer?

Set your all android path properly.

Add variable in system environment as mention below.

ANDROID_SWT : C:\Users\chetan\AppData\Local\Android\Sdk\tools\lib\x86_64

ANDROID_HOME : C:\Users\chetan\AppData\Local\Android\Sdk

ANDROID_PLATFORM_TOOLS : C:\Users\chetan\AppData\Local\Android\Sdk\platform-tools

Add below mention Path in Path Variable in system environment.

C:\Program Files\Java\jdk\bin;

C:\Users\chetan\AppData\Local\Android\Sdk\tools\bin;

C:\Users\chetan\AppData\Local\Android\Sdk\tools;

C:\Users\chetan\AppData\Local\Android\Sdk\platform-tools;

C:\Program Files\nodejs\node_modules\npm\bin;

C:\Users\chetan\AppData\Local\Android\Sdk;

C:\Users\chetan\AppData\Local\Android\Sdk\tools\lib\x86_64\swt.jar;

Pre-Check - Verify the java Version installed in your system.
VERIFY - java -version

java version "1.8.0_221" Java(TM) SE Runtime Environment (build 1.8.0_221-b11) Java HotSpot(TM) 64-Bit Server VM (build 25.221-b11, mixed mode)

If this message appears that means you have JAVA 8 install and uiautomatorviewer only supports till JAVA 8.

So install JAVA 8 from here and if you already have JAVA install down grade it to JAVA 8