How to Create and Use Global Variables in Java?

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In Java, there is no global keyword, but we can use a public static variable to referring a global variable.

Examples

For example, you can create a global variable in Java like:

UserService.java

import java.util.HashMap;
import java.util.Map;

public class UserService {
    public static Map < String, String > cache = new HashMap < > (); // GLOBAL VARIABLE
    public static final String GLOBAL_USER_NAME = "RAMESH"; // GLOBAL VARIABLE
    public static final int ID = 100; // GLOBAL VARIABLE

    public static Map < String, String > getCache() {
        return cache;
    }

    // Put data in global cache variable
    public static void putCache(String key, String value) {
        cache.put(key, value);
    }
}

GlobalVariableDemo.java

Below Java program demonstrates how to use the above created global variables. Note that you can also write data to global variables (refer cache global variable)
package com.javaguides.websocketdemo.model;

import java.util.Map;
import java.util.Map.Entry;

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

        // Put data in global variable
        UserService.putCache("key1", "value1");
        UserService.putCache("key2", "value2");
        UserService.putCache("key3", "value3");

        // Access global variable
        Map < String, String > map = UserService.cache;
        for (Entry < String, String > entry: map.entrySet()) {
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
        }

        // Access GLOBAL_USER_NAME variable
        System.out.println(UserService.GLOBAL_USER_NAME);

        // Access ID global variable

        System.out.println(UserService.ID);
    }
}
Output:
key1
value1
key2
value2
key3
value3
RAMESH
100

References


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