以Java输出（System.out.println（））

Question

In Java :

System.out.println('c' + "Hello world" + 1);

gives

cHello world1

but

System.out.println('c' + 1 + "Hello world");   

gives

100Hello world

ie c is converted to its ASCII character.What rule does Java use for this?Can someone tell me the set of rules which I can follow to predict the output as this has become quite confusing for me.

Answer 1

The + operator becomes String concatenation operator only if the left-hand side is the String . Otherwise it remains the additive operator as per docs .

In your example 'c' is a char literal, which gets promoted to int during addition. Do note that c is 99, not 119 as in your example so the output is 100Hello world .

Answer 2

because char in Java play two roles one as a String when you concatenate it with a String and the second as an int when you sum it with another numeric value.

So in your case :

System.out.println('c' + 1 + "Hello world");

Is equivalent to :

System.out.println(('c' + 1) + "Hello world");
                   ^       ^

where 'c' transform it to 99 :

System.out.println((99 + 1) + "Hello world");
                   ^^^    ^ 

For that you get :

100Hello world