The @Override annotation.
Figure 508. Overriding Object.toString() 
public class Shape {
double x, y;
...
@Override // Promise: Subsequent method overrides Object.toString();
public String toString() {
return "(" + x + "|" + y + ")";
}
}Figure 509. @Override: Easy compile time error detection
public class Shape {
double x, y;
...
@Override // Error: method does not override a method from a supertype
public String toString(int value) {
return "(" + x + "|" + y + ")";
}
}Explanation: The given method does not override Object.toString().
