Question

I want a ConcurrentHashMap that have Integer key and Object value ( some value of map are Integer and another is String).
Is this the correct way to init and use my table ?

ConcurrentHashMap table=new ConcurrentHashMap<Integer, Comparable>();
        table.put(new Integer(1), new String("nodata"));
        table.put(new Integer(2), new Integer(23));

Answer 1

A few points

• You don’t need to autobox int values and wrapping a String literal is pointless.
• You need to keep the generic type on the left, but using an interface is preferred.
• You would only use Comparable for comparing objects. However, you can’t compare objects of different types in general so this is more confusing than useful.

.

Map<Integer, Object> table = new ConcurrentHashMap<>();
table.put(1, "nodata");
table.put(2, 23);

You might want the following if you need the additional methods ConcurrentMap provides.

ConcurrentMap<Integer, Object> table = new ConcurrentHashMap<>();

This appears to be a case of object denial. Using an Object is likely to be a better choice.

class MyData {
    private String text;
    private int number;

    MyData(String text, int number) {
        this.text = text;
        this.number = number;
    }

    public synchronized String getText() {
        return text;
    }

    public synchronized void setText(String text) {
        this.text = text;
    }

    public synchronized int getNumber() {
        return number;
    }

    public synchronized void setNumber(int number) {
        this.number = number;
    }
}

MyData data = new MyData("nodata", 23);

---

For a concurrent version of the same.

class MyData {
    private final AtomicReference<String> text;
    private final AtomicInteger number;

    MyData(String text, int number) {
        this.text = new AtomicReference<String>(text);
        this.number = new AtomicInteger(number);
    }

    public String getText() {
        return text.get();
    }

    public void setText(String text) {
        this.text.set(text);
    }

    public int getNumber() {
        return number.get();
    }

    public void setNumber(int number) {
        this.number.set(number);
    }
}