# [Java (OpenJDK 8)], 134 bytes

<!-- language-all: lang-java -->

    a->{int b=a.length,i=0,j=0;for(;i++<b;){for(;j<b;j++){if(a[j].length()!=b||a[i].charAt(j)!=a[j].charAt(i))return false;}}return true;}

[Try it online!][TIO-jkrr7qxy]

[Java (OpenJDK 8)]: http://openjdk.java.net/
[TIO-jkrr7qxy]: https://tio.run/##tU/BboJAFLz7Fa@cdoMS75Qmm0oTEySmeGmMhwcuuhQXsyw2DfLt9Gmwp5r04ml29s17M1PgCSfVUepi@9lnJdY1LFDpdgSgtJUmx0xC3KZVVUrUYFhijdK79QaQ@x2paotWZRCDDqDHyUtLa5AG6JVS7@x@rILpuAimfl4Z5ivXfU593l5JQc/CdXmrcobrYjNsMP4UpOczrtXGy/ZohGUFfV0VA1ecG2kboyHHspZ@1w3UmoZY71OuY5OWlGuId6rUFg5U7Dc/8ktHgOS7tvLgVY31jjSxpWbaM0zLL7hJW@dtHoXO2Jm/hjOCKBQXCGezD6fj3L935/7kDwfxvnqwA3VIHmuRLEWyoKMEK0EokmUYEyarMIwIFyKO/uHWjbr@Bw "Java (OpenJDK 8) – Try It Online"

### Explanation:

    int b=a.length,i=0,j=0;                               //Create Variables
    for(;i++<b;){for(;j<b;j++){                           //Nested Loop
    if(a[j].length()!=b||a[i].charAt(j)!=a[j].charAt(i))  //Is the grid valid?
        return false;                                     //if not, return false
    }}
    return true;                                     //if it gets this far, return true