在Java编程中,有些知识 并不能仅通过语言规范或者标准API文档就能学到的。在本文中,我会尽量收集一些最常用的习惯用法,特别是很难猜到的用法。(Joshua Bloch的《Effective Java》对这个话题给出了更详尽的论述,可以从这本书里学习更多的用法。)
我把本文的所有代码都放在公共场所里。你可以根据自己的喜好去复制和修改任意的代码片段,不需要任何的凭证。
- 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();
- }
下面的三个例子使用了不同的方式完成了同样的事情。
实现Runnnable的方式:
- void startAThread0() {
- new Thread(new MyRunnable()).start();
- }
- class MyRunnable implements Runnable {
- public void run() {
- ...
- }
- }
继承Thread的方式:
- void startAThread1() {
- new MyThread().start();
- }
- class MyThread extends Thread {
- public void run() {
- ...
- }
- }
匿名继承Thread的方式:
- void startAThread2() {
- new Thread() {
- public void run() {
- ...
- }
- }.start();
- }
I/O流例子:
- void writeStuff() throws IOException {
- OutputStream out = new FileOutputStream(...);
- try {
- out.write(...);
- } finally {
- out.close();
- }
- }
锁例子:
- 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();
- ...
- }
使用循环:
- // Fill each element of array 'a' with 123
- byte[] a = (...);
- for (int i = 0; i < a.length; i++)
- a[i] = 123;
(优先)使用标准库的方法:
- Arrays.fill(a, (byte) 123);
使用循环:
- // 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];
(优先)使用标准库的方法:
- System.arraycopy(a, 3, b, 6, 8);
使用循环(扩大规模):
- // 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;
使用循环(减小规模):
- // 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;
(优先)使用标准库的方法:
- 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)
- };
- }
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来源: https://cloud.tencent.com/developer/article/1006774?fromSource=gwzcw.701302.701302.701302