JAVA

java pass by reference

// Java is always pass-by-value. When passing a reference variable, 
// a copy of the value of the pointer was passed, not the object itself. 

import java.util.Arrays;
class Dog {
    public String name;
    public Dog() {}     //default constructor
    public Dog(String name) {this.name = name;}
}
public class Main {
    public static void update_obj(Dog myDog) {
        myDog.name = "Changed";
    }
    public static void update_obj_v2(Dog myDog) {
        myDog = new Dog();
        myDog.name = "Changed v2";
    }
    public static void update_int(int i) {i++;}
    public static void update_Integer(Integer i) {i++;}
    public static void update_String_to_lower(String str) {str.toLowerCase();}
    public static void update_array(String[] ary) {ary[0] = "Changed";}

    public static void main(String[] args) {

        // ---------- Custom mutable objects, arrays, changed --------------------------------
        Dog max = new Dog("Max");
        update_obj(max);
        System.out.println("Dog's name is now: " + max.name);   //Changed

        Dog fido = new Dog("Fido");
        Dog fido_alias = fido;
        update_obj_v2(fido);
        System.out.println("Dog's name is now (v2): " + fido.name);     // Fido
        System.out.println("Fido object address has not changed (v2): " + String.valueOf(fido == fido_alias));  // True

        String[] fruits = {"Apple", "Orange"};
        update_array(fruits);
        System.out.println(Arrays.toString(fruits));    // [Changed, Orange]

        // ---------- Primitives, Immutable objects, NOT changed ------------------------------
        int i = 1;
        System.out.println("int before update: " + i); // 1
        update_int(i);
        System.out.println("int after update: " + i);  // 1

        Integer j = 1;
        System.out.println("Integer j before update: " + j); // 1
        update_Integer(j);
        System.out.println("Integer j after update: " + j);  // 1

        Integer k = 2;
        k++;
        System.out.println(k);      // 3

        String word = "SDSE";
        System.out.println("String before update: " + word);    //SDSE
        update_String_to_lower(word);
        System.out.println("String after update: " + word);     //SDSE
    }
}

is java pass by value or pass by reference

Both basic data types and Objects in java are pass by value. 
The difference is the value held by Objects in Java is their reference.
So the answer is: Java is always pass by value.