Final answer:
The code 'System. out. print ln("Sum=" + 4 + 5);' outputs "Sum=45" to the screen, as it processes string concatenation, not numerical addition.
Step-by-step explanation:
Concatenation is the process of appending one string to the end of another string. You concatenate strings by using the + operator. For string literals and string constants, concatenation occurs at compile time; no run-time concatenation occurs. For string variables, concatenation occurs only at run time.
The code System.out.println("Sum=" + 4 + 5) prints a string concatenation to the output screen. When executing the code, Java processes the concatenation from left to right. Initially, the integer 4 is coerced to a String and concatenated with "Sum=" resulting in "Sum=4". Afterward, the integer 5 is also coerced into a String and concatenated to the result, leading to the final output "Sum=45" on the screen. This happens because the plus operator (+) in Java is interpreted as the String concatenation operator when one of the operands is a String, which takes precedence over arithmetic addition in this context.