Implicit type casting in Java

Question

I know type casting is done automatically in Java for lower precision primitive type to higher precision. For example in this code :

int i = 20;
int j = 40;
float k = i + j; //explicit casting not required

My question is, what actually happens internally? In the third statement, do the values of i and j individually get casted to float and then added together?

Or the addition is done first in int type and then the result of addition is casted into float?

Answer 1

Let's take a look!

$ cat > temp.java
class temp {
    public void f() {
        int i = 20;
        int j = 40;
        float k = i + j; //explicit casting not required
    }
}

$ javac temp.java
$ javap -c temp
Compiled from "temp.java"
class temp {
  temp();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public void f();
    Code:
       0: bipush        20
       2: istore_1
       3: bipush        40
       5: istore_2
       6: iload_1
       7: iload_2
       8: iadd
       9: i2f
      10: fstore_3
      11: return
}

As you can see, first they are added as integers (instruction 8), then casted to a float (instruction 9).