Semantic errors indicate an improper use of Java statements.
Let us see some examples of semantic errors.
Example 1: Use of a non-initialized variable:
int i; i++; // the variable i is not initialized
Example 2: Type incompatibility:
int a = "hello"; // the types String and int are not compatible
Example 3: Errors in expressions:
String s = "..."; int a = 5 - s; // the - operator does not support arguments of type String
Example 4: Unknown references:
Strin x; // Strin is not defined system.out.println("hello"); // system is not defined String s; s.println(); // println is not a method of the class String
Example 5: Array index out of range (dynamic semantic error)
int v = new int; v = 100; // 10 is not a legal index for an array of 10 elements
The array v has been created with 10 elements (with indexes ranging from 0 to 9), and we are trying to access the element with index 10, which does not exist. This type of error is not caught during compilation, but causes an exception to be thrown at runtime.