Java函数习惯用法详解

class Person {
 String name;
 int birthYear;
 byte[] raw;
 public boolean equals(Object obj) {
  if (!obj instanceof Person)
   return false;
 
  Person other = (Person)obj;
  return name.equals(other.name)
    && birthYear == other.birthYear
    && Arrays.equals(raw, other.raw);
 }
 public int hashCode() { ... }
}

class Person {
 String a;
 Object b;
 byte c;
 int[] d;
 public int hashCode() {
  return a.hashCode() + b.hashCode() + c + Arrays.hashCode(d);
 }
 public boolean equals(Object o) { ... }
}

class Person implements Comparable<Person> {
 String firstName;
 String lastName;
 int birthdate;
 // Compare by firstName, break ties by lastName, finally break ties by birthdate
 public int compareTo(Person other) {
  if (firstName.compareTo(other.firstName) != 0)
   return firstName.compareTo(other.firstName);
  else if (lastName.compareTo(other.lastName) != 0)
   return lastName.compareTo(other.lastName);
  else if (birthdate < other.birthdate)
   return -1;
  else if (birthdate > other.birthdate)
   return 1;
  else
   return 0;
 }
}

class Values implements Cloneable {
 String abc;
 double foo;
 int[] bars;
 Date hired;
 
 public Values clone() {
  try {
   Values result = (Values)super.clone();
   result.bars = result.bars.clone();
   result.hired = result.hired.clone();
   return result;
  } catch (CloneNotSupportedException e) { // Impossible
   throw new AssertionError(e);
  }
 }
}

// join(["a", "b", "c"]) -> "a and b and c"
String join(List<String> strs) {
 StringBuilder sb = new StringBuilder();
 boolean first = true;
 for (String s : strs) {
  if (first) first = false;
  else sb.append(" and ");
  sb.append(s);
 }
 return sb.toString();
}

Random rand = new Random();
// Between 1 and 6, inclusive
int diceRoll() {
 return rand.nextInt(6) + 1;
}

void filter(List<String> list) {
 for (Iterator<String> iter = list.iterator(); iter.hasNext(); ) {
  String item = iter.next();
  if (...)
   iter.remove();
 }
}

String reverse(String s) {
 return new StringBuilder(s).reverse().toString();
}

void startAThread0() {
 new Thread(new MyRunnable()).start();
}
class MyRunnable implements Runnable {
 public void run() {
  ...
 }
}

void startAThread1() {
 new MyThread().start();
}
 class MyThread extends Thread {
 public void run() {
  ...
 }
}

void startAThread2() {
 new Thread() {
  public void run() {
   ...
  }
 }.start();
}

void writeStuff() throws IOException {
 OutputStream out = new FileOutputStream(...);
 try {
  out.write(...);
 } finally {
  out.close();
 }
}

void doWithLock(Lock lock) {
 lock.acquire();
 try {
  ...
 } finally {
  lock.release();
 }
}

InputStream in = (...);
try {
 while (true) {
  int b = in.read();
  if (b == -1)
   break;
  (... process b ...)
 }
} finally {
 in.close();
}

InputStream in = (...);
try {
 byte[] buf = new byte[100];
 while (true) {
  int n = in.read(buf);
  if (n == -1)
   break;
  (... process buf with offset=0 and length=n ...)
 }
} finally {
 in.close();
}

BufferedReader in = new BufferedReader(
  new InputStreamReader(new FileInputStream(...), "UTF-8"));
try {
 while (true) {
  String line = in.readLine();
  if (line == null)
   break;
  (... process line ...)
 }
} finally {
 in.close();
}

PrintWriter out = new PrintWriter(
  new OutputStreamWriter(new FileOutputStream(...), "UTF-8"));
try {
 out.print("Hello ");
 out.print(42);
 out.println(" world!");
} finally {
 out.close();
}

int factorial(int n) {
 if (n < 0)
  throw new IllegalArgumentException("Undefined");
 else if (n >= 13)
  throw new ArithmeticException("Result overflow");
 else if (n == 0)
  return 1;
 else
  return n * factorial(n - 1);
}

int findIndex(List<String> list, String target) {
 if (list == null || target == null)
  throw new NullPointerException();
 ...
}

void frob(byte[] b, int index) {
 if (b == null)
  throw new NullPointerException();
 if (index < 0 || index >= b.length)
  throw new IndexOutOfBoundsException();
 ...
}

void frob(byte[] b, int off, int len) {
 if (b == null)
  throw new NullPointerException();
 if (off < 0 || off > b.length
  || len < 0 || b.length - off < len)
  throw new IndexOutOfBoundsException();
 ...
}

// Fill each element of array 'a' with 123
byte[] a = (...);
for (int i = 0; i < a.length; i++)
 a[i] = 123;

// Copy 8 elements from array 'a' starting at offset 3
// to array 'b' starting at offset 6,
// assuming 'a' and 'b' are distinct arrays
byte[] a = (...);
byte[] b = (...);
for (int i = 0; i < 8; i++)
 b[6 + i] = a[3 + i];

// Make array 'a' larger to newLen
byte[] a = (...);
byte[] b = new byte[newLen];
for (int i = 0; i < a.length; i++) // Goes up to length of A
 b[i] = a[i];
a = b;

// Make array 'a' smaller to newLen
byte[] a = (...);
byte[] b = new byte[newLen];
for (int i = 0; i < b.length; i++) // Goes up to length of B
 b[i] = a[i];
a = b;

a = Arrays.copyOf(a, newLen);

int packBigEndian(byte[] b) {
 return (b[0] & 0xFF) << 24
    | (b[1] & 0xFF) << 16
    | (b[2] & 0xFF) << 8
    | (b[3] & 0xFF) << 0;
}
 
int packLittleEndian(byte[] b) {
 return (b[0] & 0xFF) << 0
    | (b[1] & 0xFF) << 8
    | (b[2] & 0xFF) << 16
    | (b[3] & 0xFF) << 24;
}

byte[] unpackBigEndian(int x) {
 return new byte[] {
  (byte)(x >>> 24),
  (byte)(x >>> 16),
  (byte)(x >>> 8),
  (byte)(x >>> 0)
 };
}
 
byte[] unpackLittleEndian(int x) {
 return new byte[] {
  (byte)(x >>> 0),
  (byte)(x >>> 8),
  (byte)(x >>> 16),
  (byte)(x >>> 24)
 };
}