When we are in a for loop,
for(int i =0; i< 10 ; i++)
{
System.out.println(i + 1);
}
will execute 1-10
However, if I change System.out.println to lets say a function passed such as
for(int i=0;i<10;i++)
{
passed( "Row" + (i+1));
}
Where passed is
public static void passed(String check) {
System.out.println(check + "Passed");
}
It executes
01 Passed 11 Passed 21 Passed 31 Passed.... 41 51 61
and so forth
Can anyone explain why does it pass the value first and skip the math?
System.out.println(i + 1); --> println(int) called
System.out.println(check + "Passed"); --> println(String) is called.
java code :
public static void main(String[] args) {
int check = 0;
System.out.println(check + "Passed"); //StringBuilder operation int + string concatenated as Strings then println is called.
System.out.println(check + 5); // int + int concatenated as int, then println is called
}
byte code :
0: iconst_0
1: istore_1
2: getstatic #16; //Field java/lang/System.out:Ljava/io/PrintStream;
5: new #22; //class java/lang/StringBuilder
8: dup
9: iload_1
10: invokestatic #24; //Method java/lang/String.valueOf:(I)Ljava/lang/Str
ing;
// use StringBuilder and invoke println()
13: invokespecial #30; //Method java/lang/StringBuilder."<init>":(Ljava/la
ng/String;)V
16: ldc #33; //String Passed
18: invokevirtual #35; //Method java/lang/StringBuilder.append:(Ljava/lang
/String;)Ljava/lang/StringBuilder;
21: invokevirtual #39; //Method java/lang/StringBuilder.toString:()Ljava/l
ang/String;
24: invokevirtual #43; //Method java/io/PrintStream.println:(Ljava/lang/St
ring;)V --> string println called
27: getstatic #16; //Field java/lang/System.out:Ljava/io/PrintStream;
30: iload_1 // load value of check(int)
31: iconst_5 ----> constant 5
32: iadd ----> add constant 5 and value of check and then invoke method
33: invokevirtual #48; //Method java/io/PrintStream.println:(I)V --> integer println called
36: return
println (int) method, it would give the same result: int -> (boxing) -> Integer <- Object, while there is method println (Object), which just runs toString on it.
Java apply a particular rule when it comes to mixing String and any numerics (int, double, ...):
System.out.println(1+1+""); //prints 2
however
System.out.println(""+1+1);//prints 11
How's that ?
Java will read from right to left and give priority to String. So, in the first case Java will evaluate int + int = int before evaluating int + String = String. But in the second example, it will be String + int = String being first evaluated then String + int = String.
When you are calling System.out.println directly, the run time can determine that the value being passed is an int and that addition should be performed before the println (for int values) is executed. When you are wrapping that call up in a function which takes a String parameter and passing your int value into that function, the int value is being coerced into a String value as passed is called and then concatenation is being done instead of addition before the println (for String values) is executed.
"Row" + (i+1)or"Row" + i+1?