Why does the System class not need to be imported?

public class Test
{
// Main method
public static void main(String[] args) {
/** Display output */
System.out.println("Welcome to Java");
}
}

 public class Test {
  // Main method 
  public static void main(String[] args) {
    /** Display outpput */
    System.out.println("Welcome to Java");
  }
}

Run Time Error: Run Time errors occur or we can say, are detected during the execution of the program. Sometimes these are discovered when the user enters an invalid data or data which is not relevant. Runtime errors occur when a program does not contain any syntax errors but asks the computer to do something that the computer is unable to reliably do. During compilation, the compiler has no technique to detect these kinds of errors. It is the JVM (Java Virtual Machine) which detects it while the program is running. To handle the error during the run time we can put our error code inside the try block and catch the error inside the catch block.

Compile Time Error: Compile Time Errors are those errors which prevent the code from running because of an incorrect syntax such as a missing semicolon at the end of a statement or a missing bracket, class not found, etc. These errors are detected by the java compiler and an error message is displayed onto the screen while compiling. Compile Time Errors are sometimes also referred to as Syntax errors. These kind of errors are easy to spot and rectify because the java compiler finds them for you. The compiler will tell you which piece of code in the program got in trouble and its best guess as to what you did wrong. Usually, the compiler indicates the exact line where the error is, or sometimes the line just before it, however, if the problem is with incorrectly nested braces, the actual error may be at the beginning of the block. In effect, syntax errors represent grammatical errors in the use of the programming language.

Logical Error: A logic error is when your program compiles and executes, but does the wrong thing or returns an incorrect result or no output when it should be returning an output. These errors are detected neither by compiler nor by JVM. The Java system has no idea what your program is supposed to do, so it provides no additional information to help you find the error. Logical errors are also called Semantic Errors. These errors are caused due to an incorrect idea or concept used by a programmer while coding. Syntax errors are grammatical errors whereas, logical errors are errors arising out of an incorrect meaning.

For example: if a programmer accidentally adds two variables when he or she meant to divide them, the program will give no error and will execute successfully but with an incorrect result.

1 public class Welcome {
2 public void Main(String[] args) {
3 System.out.println('Welcome to Java!);
4 }
5 }

Line 2. Main should be main. 
Line 2. static is missing.
Line 3: Welcome to Java! should be enclosed inside double quotation marks.
Line 5: The last ) should be }. 

1 public static void main(String[] args) {
2 }
3 public class Welcome {
4 System.out.println("afternoon");
5 System.out.println("morning");
6 } 

public class Welcome {
  public static void main(String[] args) {
    System.out.println("morning");
    System.out.println("afternoon");
  }
}

Java is a high-level programming language originally developed by Sun Microsystems and released in 1995. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX.