8. class Sum implements Callable<Long> {
private final long from;
private final long to;
Sum(long from, long to) {
this.from = from;
this.to = to;
}
public Long call() {
long acc = 0;
for (long i = from; i <= to; i++) {
acc = acc + i;
}
return acc;
}
}
9. ExecutorService executor = Executors.newFixedThreadPool(2);
List<Future<Long>> results = executor.invokeAll(asList(
new Sum(0, 10),
new Sum(100, 1000),
new Sum(10000, 1000000)
));
for (Future<Long> result : results) {
System.out.println(result.get());
}
10. 1.0 Threads made easy
1.1
1.2
1.3
1.4
5 Concurrency made easier
6
7 Parallelism made easier
11. Sum of an array
n1 n2 n3 n4 n5 n6 n7 n8 n9 ... ... ... ...
sum1 sum2 sum3
sum1 + sum2 sum3 + (...)
total sum
16. 16
Folder word
counting task
10
5
1
Document word Document word Folder word
counting task counting task counting task
3 2
fork()
Document word Document word
n join() counting task counting task
19. No I/O
No synchronization / locks
Decompose in simple recursive tasks
Do not decompose below a threshold
Take advantage of multicores with no pain
You have more F/J candidate algorithms than
you think!
21. private void writeSomeData() throws IOException {
DataOutputStream out = new DataOutputStream(new FileOutputStream("data"));
out.writeInt(666);
out.writeUTF("Hello");
out.close();
}
22. private void writeSomeData() throws IOException {
DataOutputStream out = new DataOutputStream(new FileOutputStream("data"));
out.writeInt(666);
out.writeUTF("Hello");
out.close();
}
what if...
23. private void writeSomeData() throws IOException {
DataOutputStream out = null;
try {
out = new DataOutputStream(new FileOutputStream("data"));
out.writeInt(666);
out.writeUTF("Hello");
} finally {
if (out != null) {
out.close();
}
}
}
24. private void writeSomeData() throws IOException {
DataOutputStream out = null;
try {
out = new DataOutputStream(new FileOutputStream("data"));
out.writeInt(666);
out.writeUTF("Hello");
} finally {
if (out != null) {
out.close();
}
}
}
...this is still far from correct!
25. try (
FileOutputStream out = new FileOutputStream("output");
FileInputStream in1 = new FileInputStream(“input1”);
FileInputStream in2 = new FileInputStream(“input2”)
) {
// Do something useful with those 3 streams!
// out, in1 and in2 will be closed in any case
out.write(in1.read());
out.write(in2.read());
}
26. public class AutoClose implements AutoCloseable {
@Override
public void close() {
System.out.println(">>> close()");
throw new RuntimeException("Exception in close()");
}
public void work() throws MyException {
System.out.println(">>> work()");
throw new MyException("Exception in work()");
}
}
28. AutoClose autoClose = new AutoClose();
try {
autoClose.work();
} finally {
autoClose.close();
}
>>> work()
>>> close()
java.lang.RuntimeException: Exception in close()
at AutoClose.close(AutoClose.java:6)
at AutoClose.runWithMasking(AutoClose.java:19)
at AutoClose.main(AutoClose.java:52)
29. AutoClose autoClose = new AutoClose();
try {
autoClose.work();
} finally {
autoClose.close();
}
MyException
m asked by Run
>>> work() time Exception
>>> close()
java.lang.RuntimeException: Exception in close()
at AutoClose.close(AutoClose.java:6)
at AutoClose.runWithMasking(AutoClose.java:19)
at AutoClose.main(AutoClose.java:52)
37. try (AutoClose autoClose = new AutoClose()) {
autoClose.work();
}
>>> work()
>>> close()
MyException: Exception in work()
at AutoClose.work(AutoClose.java:11)
at AutoClose.main(AutoClose.java:16)
Suppressed: java.lang.RuntimeException: Exception in close()
at AutoClose.close(AutoClose.java:6)
at AutoClose.main(AutoClose.java:17)
38. public void compress(String input, String output)
throws IOException {
try(
FileInputStream fin = new FileInputStream(input);
FileOutputStream fout = new FileOutputStream(output);
GZIPOutputStream out = new GZIPOutputStream(fout)
) {
byte[] buffer = new byte[4096];
int nread = 0;
while ((nread = fin.read(buffer)) != -1) {
out.write(buffer, 0, nread);
}
}
}
40. Not just syntactic sugar
Clutter-free, correct code
close():
- be more specific than java.lang.Exception
- no exception if it can’t fail
- no exception that shall not be suppressed
(e.g., java.lang.InterruptedException)
49. class SomeClass<T extends Serializable & CharSequence> { }
Non-denotable type
SomeClass<?> foo = new SomeClass<String>();
SomeClass<?> fooInner = new SomeClass<String>() { };
SomeClass<?> bar = new SomeClass<>();
SomeClass<?> bar = new SomeClass<>() { };
50. class SomeClass<T extends Serializable & CharSequence> { }
Non-denotable type
SomeClass<?> foo = new SomeClass<String>();
SomeClass<?> fooInner = new SomeClass<String>() { };
SomeClass<?> bar = new SomeClass<>();
SomeClass<?> bar = new SomeClass<>() { };
No denotable type
to generate a class
71. // 123 in decimal, octal, hexadecimal and binary
byte decimal = 123;
byte octal = 0_173;
byte hexadecimal = 0x7b;
byte binary = 0b0111_1011;
// Other values
double doubleValue = 1.111_222_444F;
long longValue = 1_234_567_898L;
long longHexa = 0x1234_3b3b_0123_cdefL;
72. public static boolean isTrue(String str) {
switch(str.trim().toUpperCase()) {
case "OK":
case "YES":
case "TRUE":
return true;
case "KO":
case "NO":
case "FALSE":
return false;
default:
throw new IllegalArgumentException("Not a valid true/false string.");
}
}
73. public static boolean isTrue(String s) {
String str = s.trim().toUpperCase();
int jump = -1;
switch(str.hashCode()) {
case 2404:
if (str.equals("KO")) {
jump = 3; Bucket
}
break;
(...)
switch(jump) {
(...)
case 3:
case 4:
case 5:
return false;
default: Real code
throw new IllegalArgumentException(
"Not a valid true/false string.");
}
}
74. Oracle Technology Network (more soon...)
Fork and Join: Java Can Excel at
Painless Parallel Programming Too!
http://goo.gl/tostz
Better Resource Management with
Java SE 7: Beyond Syntactic Sugar
http://goo.gl/7ybgr
