class A {
      public int field1;
      public void method1() {
          System.out.println("A");
      }

      public void method2() {
          System.out.println("A");
      }
  }

  class B extends A {
      public int field2;
      public void method1() {
          System.out.println("B");
      }
  }

is basically equivalent to

  interface C {
      public void method1() {}
      public void method2() {}
  }
  
  class A implements C {
      public int field1;
      public void method1() {
          System.out.println("A");
      }
      public void method2() {
          System.out.println("A");
      }
  }

  class B implements C {
      public A a;
      public int field2;
      public void method1() {
          System.out.println("B");
      }
      public void method2() {
          a.method();
      }
  }

As you can see both are basically the same except one little detail. The benefit is that you don't have to write the redundant "method2" method in class B. So the only time inheritance is ever useful is when you don't want to override all methods. Now someone tells you to model everything in terms of class hierarchies even when they don't need it right now and you've negated the tiny little benefit it ever had which means not having it in the programming language actually has positive consequences.