StackOverflow DI example

di-example.java

public class A
{
    private Bable b;
    private Cable c;
    
    public A(Bable b, Cable c)
    {
        this.b = b;
        this.c = c;
    }
    
    public void doThings() {
      this.b.doBThings();
      this.c.doCThings();
    }
}


public interface Bable
{
    public void doBThings();
}

public interface Cable
{
    public void doCThings();
}

public interface Xable
{
    public void doXThings();
}

public class B implements Bable
{
    private Xable x;

    // You said B depends on C
    // I am betting B does not depend on the same aspect of C
    // that A does, so I am separating those aspects out into
    // the Cable interface (for A) and the Xable interface (for B).
    // The concrete C class happens to implement both, but B only
    // cares about the Xable contract, whereas A only cares about
    // the Cable contract.
    public B(Xable x)
    {
      this.x = x;
    }
    
    public void doBThings()
    {
      // TODO: do something B-specific

      // also use the Xable contract
      this.x.doXThings();
    }
}

public class C implements Cable, Xable
{
    public void doCThings() {}
    public void doXThings() {} 
}