Are '', zero, and null equal in PHP?

In PHP, 0 and null are equal ?! Guess the output result of the following code. I was a little surprised when I started the php language. compared with java, the output result was a little surprised $ str1, $ str2; syntax error $ str1null; $ str2; if ($ str10) echo equal; elseecho unequal; echo & lt; br & gt;, & PHP's '', 0, null equal ?!
Guess the output result of the following code. I was a little surprised when I started to use the php language and compared it with java.

// $ Str1, $ str2 = ''; // syntax error $ str1 = null; $ str2 =''; if ($ str1 = 0) echo "equal "; elseecho "not equal"; echo'
','
','
'; If ($ str2 = 0) echo "equal"; elseecho "not equal ";