Assert ,可以看作是异常处理的一种高级封装形式

1.assert 关键字
......

2.(断言)org.eclipse.core.runtime.Assert源码:

public final class Assert {
 private Assert() {
  // not allowed
 }

 public static boolean isLegal(boolean expression) {
  return isLegal(expression, ""); 
 }

 public static boolean isLegal(boolean expression, String message) {
  if (!expression)
   throw new IllegalArgumentException(message);
  return expression;
 }
 
 public static void isNotNull(Object object) {
  isNotNull(object, ""); 
 }

 public static void isNotNull(Object object, String message) {
  if (object == null)
   throw new AssertionFailedException("null argument:" + message); 
 }

 public static boolean isTrue(boolean expression) {
  return isTrue(expression, ""); 
 }

 public static boolean isTrue(boolean expression, String message) {
  if (!expression)
   throw new AssertionFailedException("assertion failed: " + message); 
  return expression;
 }
}