Boolean value in java

Hey guys, I have a little bit confused on below code and output

Main

  public class Main {

        public static void main(String[] args) {
            ClassA classA = new ClassA();
            System.out.println("====== Before =====");
            classA.checking();
            System.out.println("===== After =====");
            classA.checking();
        }
    }

Class A

public class ClassA {

    boolean b = true;

    public String checking() {
        System.out.println("B value is " + b);
        if (b = true) {
            System.out.println("B is true");
            b = false;
        } else {
            System.out.println("B is false");
        }
        return null;
    }
}

Output

====== Before =====
B value is true
B is true
===== After =====
B value is false
B is true

Why the last line of value B in After will change from false to true ?