50个常用的Java代码示例

1.输出语句：

System.out.println(Hello World!);

2.定义变量：

int x = 5;
String name = John;

3.循环语句：

for(int i = 0; i < 10; i++) {

System.out.println(i);

}

4.条件语句：

if(x > 0) {

System.out.println(x is positive);

} else if(x < 0) {

System.out.println(x is negative);

} else {

System.out.println(x is zero);

}

5.创建数组：

int[] arr = new int[5];

6.循环遍历数组：

for(int i = 0; i < arr.length; i++) {

System.out.println(arr[i]);

}

7.使用List集合：

List list = new ArrayList<>();

list.add(apple);

list.add(banana);

list.add(orange);

8.遍历List集合：

for(String fruit : list) {

System.out.println(fruit);

}

9.使用Map集合：

Map map = new HashMap<>();

map.put(apple, 1);

map.put(banana, 2);

map.put(orange, 3);

10.遍历Map集合：

for(String key : map.keySet()) {

System.out.println(key + : + map.get(key));

}

11.使用Scanner类读取用户输入：

Scanner scanner = new Scanner(System.in);

System.out.println(Enter your name:);

String name = scanner.nextLine();

System.out.println(Hello + name);

12.使用try-catch语句处理异常：

try {

// some code that might throw an exception

} catch(Exception e) {

System.out.println(An error occurred: + e.getMessage());

}

13.定义方法：

public static void sayHello() {

System.out.println(Hello);

}

14.调用方法：

sayHello();

15.方法传递参数：

public static void sayHelloTo(String name) {

System.out.println(Hello + name);

}



sayHelloTo(John);

16.定义类：

public class Person {

String name;

int age;



public Person(String name, int age) {

this.name = name;

this.age = age;

}



public void sayHello() {

System.out.println(Hello, my name is + name + and I'm + age + years old.);

}

}

17.创建类的实例：

Person person = new Person(John, 30);

18.调用对象的方法：

person.sayHello();

19.继承类：

public class Student extends Person {

String major;



public Student(String name, int age, String major) {

super(name, age);

this.major = major;

}



public void sayHello() {

System.out.println(Hello, my name is + name + , I'm + age + years old, and I'm studying + major);

}

}

Student student = new Student(Jane, 20, Computer Science);

student.sayHello();

20.实现接口：

public interface Animal {

void makeSound();

}



public class Dog implements Animal {

public void makeSound() {

System.out.println(Woof!);

}

}



Dog dog = new Dog();

dog.makeSound();

21.抛出异常：

public void doSomething() throws IOException {

// some code that might throw an IOException

}



try {

doSomething();

} catch(IOException e) {

System.out.println(An IO error occurred: + e.getMessage());

}

22.格式化字符串：

String name = John;

int age = 30;

String message = String.format(My name is %s and I'm %d years old, name, age);

System.out.println(message);

23.使用正则表达式：

String pattern = \\d+;

String text = 123abc456def789;

Pattern p = Pattern.compile(pattern);

Matcher m = p.matcher(text);

while(m.find()) {

System.out.println(m.group());

}

24.写入文件：

String content = Hello World!;

File file = new File(output.txt);

try {

FileWriter writer = new FileWriter(file);

writer.write(content);

writer.close();

} catch(IOException e) {

System.out.println(An IO error occurred: + e.getMessage());

}

25.读取文件：

File file = new File(input.txt);

try {

Scanner scanner = new Scanner(file);

while(scanner.hasNextLine()) {

String line = scanner.nextLine();

System.out.println(line);

}

scanner.close();

} catch(FileNotFoundException e) {

System.out.println(File not found: + e.getMessage());

}

26.使用日期和时间：

Date date = new Date();

DateFormat dateFormat = new SimpleDateFormat(yyyy/MM/dd HH:mm:ss);

String formattedDate = dateFormat.format(date);

System.out.println(formattedDate);

27.使用正则表达式替换字符串：

String text = Hello World!;

String pattern = l;

String replacement = -;

String replacedText = text.replaceAll(pattern, replacement);

System.out.println(replacedText);

28.使用Lambda表达式：

List list = Arrays.asList(1, 2, 3, 4, 5);

list.forEach(n -> System.out.println(n));

29.使用Stream API过滤数据：

List list = Arrays.asList(1, 2, 3, 4, 5);

list.stream()

.filter(n -> n % 2 == 0)

.forEach(n -> System.out.println(n));

30.使用Optional类避免空指针异常：

Optional optional = Optional.ofNullable(null);

String text = optional.orElse(default);

System.out.println(text);

31.使用Java集合框架之List：

List list = new ArrayList<>();

list.add(apple);

list.add(banana);

list.add(orange);

for(String item : list) {

System.out.println(item);

}

32.使用Java集合框架之Set：

Set set = new HashSet<>();

set.add(apple);

set.add(banana);

set.add(orange);

for(String item : set) {

System.out.println(item);

}

33.使用Java集合框架之Map：

Map map = new HashMap<>();

map.put(apple, 1);

map.put(banana, 2);

map.put(orange, 3);

for(Map.Entry entry : map.entrySet()) {

System.out.println(entry.getKey() + -> + entry.getValue());

}

34.使用Java集合框架之Queue：

Queue queue = new LinkedList<>();

queue.offer(apple);

queue.offer(banana);

queue.offer(orange);

while(!queue.isEmpty()) {

System.out.println(queue.poll());

}

35.使用Java集合框架之Stack：

Stack stack = new Stack<>();

stack.push(apple);

stack.push(banana);

stack.push(orange);

while(!stack.isEmpty()) {

System.out.println(stack.pop());

}

36.多线程编程：

class MyThread extends Thread {

public void run() {

System.out.println(Hello from thread + Thread.currentThread().getId());

}

}



MyThread thread = new MyThread();

thread.start();

37.使用Executor框架创建线程池：

ExecutorService executor = Executors.newFixedThreadPool(10);

for(int i = 0; i < 100; i++) {

executor.submit(() -> {

System.out.println(Hello from thread + Thread.currentThread().getId());

});

}

executor.shutdown();

38.使用ReentrantLock实现线程同步：

class Counter {

private int value = 0;

private ReentrantLock lock = new ReentrantLock();



public void increment() {

lock.lock();

try {

value++;

} finally {

lock.unlock();

}

}



public int getValue() {

return value;

}

}



Counter counter = new Counter();

executor.submit(() -> {

for(int i = 0; i < 100000; i++) {

counter.increment();

}

});

executor.submit(() -> {

for(int i = 0; i < 100000; i++) {

counter.increment();

}

});

executor.shutdown();

executor.awaitTermination(1, TimeUnit.MINUTES);

System.out.println(counter.getValue());

39.使用Semaphore实现资源共享：

Semaphore semaphore = new Semaphore(3);

for(int i = 0; i < 10; i++) {

executor.submit(() -> {

try {

semaphore.acquire();

System.out.println(Hello from thread + Thread.currentThread().getId());

Thread.sleep(1000);

semaphore.release();

} catch(InterruptedException e) {

e.printStackTrace();

}

});

}

executor.shutdown();

executor.awaitTermination(1, TimeUnit.MINUTES);

40.使用CountDownLatch实现线程同步：

CountDownLatch latch = new CountDownLatch(2);

executor.submit(() -> {

System.out.println(Task 1 is running);

Thread.sleep(1000);

latch.countDown();

});

executor.submit(() -> {

System.out.printlnTask 2 is running);

Thread.sleep(2000);

latch.countDown();

});

latch.await();

System.out.println(All tasks are completed);

41. 使用CyclicBarrier实现线程同步：

CyclicBarrier barrier = new CyclicBarrier(2, () -> {

System.out.println(Barrier action is running);

});

executor.submit(() -> {

System.out.println(Task 1 is running);

Thread.sleep(1000);

barrier.await();

});

executor.submit(() -> {

System.out.println(Task 2 is running);

Thread.sleep(2000);

barrier.await();

});

executor.shutdown();

executor.awaitTermination(1, TimeUnit.MINUTES);

42.使用Future和Callable实现异步编程：

class MyCallable implements Callable {

public String call() throws Exception {

Thread.sleep(1000);

return Hello from thread + Thread.currentThread().getId();

}

}



Future future = executor.submit(new MyCallable());

System.out.println(future.get());

43.使用Java8的Stream API进行集合操作：

List list = Arrays.asList(1, 2, 3, 4, 5);

int sum = list.stream().filter(x -> x % 2 == 0).mapToInt(x -> x).sum();

System.out.println(sum);

44.使用Java8的Optional类处理可能为空的对象：

Optional optional = Optional.ofNullable(null);

System.out.println(optional.orElse(default value));

45.使用Java8的Lambda表达式进行函数式编程：

interface MyFunction {

int apply(int x, int y);

}



MyFunction add = (x, y) -> x + y;

System.out.println(add.apply(1, 2));

46.使用Java8的方法引用简化Lambda表达式：

List list = Arrays.asList(apple, banana, orange);

list.forEach(System.out::println);

47.使用Java8的默认方法为接口提供默认实现：

interface MyInterface {

default void sayHello() {

System.out.println(Hello from MyInterface);

}

}



class MyClass implements MyInterface {

}



MyClass obj = new MyClass();

obj.sayHello();

48.使用Java8的接口中的静态方法：

interface MyInterface {

static void sayHello() {

System.out.println(Hello from MyInterface);

}

}



MyInterface.sayHello();

49.使用Java8的日期和时间API：

LocalDateTime now = LocalDateTime.now();

DateTimeFormatter formatter = DateTimeFormatter.ofPattern(yyyy-MM-dd HH:mm:ss);

String formatted = now.format(formatter);

System.out.println(formatted);

50.使用Java8的Optional和Stream API组合进行复杂的操作：

class Person {

private String name;

private Optional

address;





public Person(String name, Optional

address) {



this.name = name;

this.address = address;

}



public String getName() {

return name;

}



public Optional

getAddress() {



return address;

}

}



class Address {

private String city;



public Address(String city) {

this.city = city;

}



public String getCity() {

return city;

}

}



List list = Arrays.asList(

new Person(Alice, Optional.of(new Address(New York))),

new Person(Bob, Optional.empty()),

new Person(Charlie,Optional.of(new Address(Los Angeles)))

);



String city = list.stream()

.filter(person -> person.getName().startsWith(B))

.flatMap(person -> person.getAddress().stream())

.map(Address::getCity)

.findFirst()

.orElse(Unknown);



System.out.println(city);

Optional和Stream API组合进行复杂的操作：

class Person {

private String name;

private Optional

address;





public Person(String name, Optional

address) {



this.name = name;

this.address = address;

}



public String getName() {

return name;

}



public Optional

getAddress() {



return address;

}

}



class Address {

private String city;



public Address(String city) {

this.city = city;

}



public String getCity() {

return city;

}

}



List list = Arrays.asList(

new Person(Alice, Optional.of(new Address(New York))),

new Person(Bob, Optional.empty()),

new Person(Charlie,Optional.of(new Address(Los Angeles)))

);



String city = list.stream()

.filter(person -> person.getName().startsWith(B))

.flatMap(person -> person.getAddress().stream())

.map(Address::getCity)

.findFirst()

.orElse(Unknown);



System.out.println(city);

以上就是50个常用的Java代码示例，希望对你有所帮助。