AvoidingMutableState.java

class SomeThing {
    final Dependency1 dependency1;
    Dependency2 dependency2;
    
    Something(Dependency1 dependency1){
        this.dependency1 = dependency1;
    }
    
    void setDependency2(Dependency2 dependency2){
        this.dependency2 = dependency2;
    }
    
    void somethingThatNeedsBoth(){
       dependency1.doIt();
       dependency2.doIt(); //may not be set, order of calls is important: bad OO
    }
}

// Instead setting second dependency returns another object

class SomeThing {
    final Dependency1 dependency1;
    
    Something(Dependency1 dependency1){
        this.dependency1 = dependency1;
    }
    
    SomeThing2 setDependency2(Dependency2 dependency2){
        return new SomeThing2(dependency2);
    }
    
    class SomeThing2 {
        final Dependency2 dependency2;
    
        SomeThing2(Dependency2 dependency2){
            this.dependency2 = dependency2;
        }
    
        void somethingThatNeedsBoth(){
           dependency1.doIt();
           dependency2.doIt(); //both must have be set
        }
    }
}