import org.checkerframework.checker.nullness.qual.Nullable;

class ChainAssignment {
    @Nullable Object a;
    @Nullable Object b;
    Object x = new Object();
    Object y = new Object();

    void m1() {
        a = b = new Object();
    }

    void m2() {
        this.a = this.b = new Object();
    }

    void m3() {
        a = this.b = new Object();
    }

    void m4() {
        this.a = b = new Object();
    }

    void n1() {
        // :: error: (assignment.type.incompatible)
        x = y = null;
    }

    void n2() {
        // :: error: (assignment.type.incompatible)
        this.x = this.y = null;
    }

    void n3() {
        // :: error: (assignment.type.incompatible)
        x = this.y = null;
    }

    void n4() {
        // :: error: (assignment.type.incompatible)
        this.x = y = null;
    }
}