[Java] 5 Basic questions

1 what is "Arbitrary Number of Arguments" : 可变参数 ： ...
It allows the method to take one or more parameters of the same type.  f(int ...a) --> f(int[] a)

2what is assert  :  to assert if a expression is true
 ex : assert(myValue == 0); if true, nothing; if false, throws AssertionError
is often used for assert input parameters

3 when the GC runs :  heap stack no enough and CPU is free. JVM uses System.gc() to call GC
   when memory is full occupied and there is no object can do the GC, : OutOfMemoryException.
   before the object is removed from memory, finalize() will be called. Not use finalize in your code.

4 static initialization block  static { ... }
static block, just call one time during compilation

public class InitializerExamples {

static int count;

int i;

static{

//This is a static initializers. Run only when Class is first loaded.

//Only static variables can be accessed

System.out.println("Static Initializer");

//i = 6;//COMPILER ERROR

System.out.println("Count when Static Initializer is run is " + count);

}

public static void main(String[] args) {

InitializerExamples example = new InitializerExamples();

InitializerExamples example2 = new InitializerExamples();

InitializerExamples example3 = new InitializerExamples();

}

}

sout:

Static Initializer

Count when Static Initializer is run is 0.

 initialization block  { ... }

block is called every time we create an object

public class InitializerExamples {

static int count;

int i;

{

//This is an instance initializers. Run every time an object is created.

//static and instance variables can be accessed

System.out.println("Instance Initializer");

i = 6;

count = count + 1;

System.out.println("Count when Instance Initializer is run is " + count);

}

public static void main(String[] args) {

InitializerExamples example = new InitializerExamples();

InitializerExamples example1 = new InitializerExamples();

InitializerExamples example2 = new InitializerExamples();

}

}

5 Tokenize : 令牌化
indeed, it's splitting a string : ac;bd;def;e---> ac，bd，def, e

private static void tokenize(String string,String regex) {

String[] tokens = string.split(regex);

System.out.println(Arrays.toString(tokens));

}

Using Scanner to realize :

private static void tokenizeUsingScanner(String string,String regex) {

Scanner scanner = new Scanner(string);

scanner.useDelimiter(regex);

List<String> matches = new ArrayList<String>();

while(scanner.hasNext()){

matches.add(scanner.next());

}

System.out.println(matches);

}