1, Class as member variable

//Define Computer class
class Computer{
    private String CPU;
    private String RAM;
	//Parameterless construction method, getter and setter methods
    public Computer() {}
    public Computer(String CPU, String RAM) {this.CPU = CPU;this.RAM = RAM;}
    public String getCPU() {return CPU;}
    public void setCPU(String CPU) {this.CPU = CPU;}
    public String getRAM() {return RAM;}
    public void setRAM(String RAM) {this.RAM = RAM;}
}

//Define the Person class
class Person{
    private String name;
    //Class as member variable
    private Computer computer;
    //Parameterless construction method, getter and setter methods
    public Person() {}
    public Person(String name, Computer computer) {this.name = name;this.computer = computer;}
    public String getName() {return name;}
    public void setName(String name) {this.name = name;}
    public Computer getComputer() {return computer;}
    public void setComputer(Computer computer) {this.computer = computer;}

    //Define a member method for printing information
    public void useComputer(){
        System.out.println(name+"The configuration of the computer in use is,\nCPU: "+computer.getCPU()+"\n Memory:"+computer.getRAM());
    }
}

public class Test {
    public static void main(String[] args) {
        //Assign values to variables of Computer through construction method
        Computer computer = new Computer("i9-9900k","32G");
        //Assign a value to the variable of Person through the construction method
        Person person = new Person("Zhang Sanfeng",computer);
        //Use useComputer method to view data transfer results
        person.useComputer();
    }
}

Operation results

2, Interface as member variable

interface Use{
    void use();
}
//Create the implementation class of the interface
class UseComputerImpl implements Use{
    @Override
    public void use() {System.out.println("Using computer");}
}

//Define a People class with the interface as a member variable
class People{
    private String name;
    //Interface type as member variable
    private Use use;
	//No parameter and parameter construction method, because getter and setter methods are not used, which is omitted here. In normal use, it is not recommended to omit
    public People() {}
    public People(String name, Use use) {this.name = name;this.use = use;}

    //Create a member method that uses the interface to print information
    public void useComputer(){
        System.out.print(name);
        //Using interface objects, calling implementation class methods
        use.use();
    }
}

//Test class, test the code written
public class Test {
    public static void main(String[] args) {
        //Create implementation class objects (automatically transitioning up to interface types)
        Use use = new UseComputerImpl();
        //Pass data to member variables using People's parametric construction
        People people = new People("Zhang Sanfeng",use);
        //Use the object of People to call the useComputer method to view the data transfer results
        people.useComputer();
    }
}

Operation results

Let's expand

Create a new Test2 test class. The above code remains unchanged

public class Test2 {
    public static void main(String[] args) {

        //Using anonymous inner classes to create interface objects
        Use use = new Use() {
            @Override
            public void use() {
                System.out.println("Using computer");
            }
        };
        //Pass data to member variables using People's parametric construction
        People peopleOne = new People("Zhang San",use);
        //Use the object of People to call the useComputer method to view the data transfer results
        peopleOne.useComputer();

//=====================================================
        
        //Use anonymous inner class and anonymous object to pass parameters
        People peopleTwo = new People("Li Si", new Use() {
            @Override
            public void use() {
                System.out.println("Using computer");
            }
        });
        //Use the object of People to call the useComputer method to view the data transfer results
        peopleTwo.useComputer();
    }
}

Operation results