How To Do In Java
The point is to break the rule everyday.
Use Java 8 till the world ends
2032：I still use Java 8.
Write once,run nowwhere
Use maven rather than gradle, install tons of dependencies even you just wanna hello world
<!-- https://mvnrepository.com/artifact/org.springframework/spring-context -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>5.2.4.RELEASE</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.springframework/spring-core -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>5.2.4.RELEASE</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.springframework/spring-beans -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>5.2.4.RELEASE</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.springframework/spring-web -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
<version>5.2.4.RELEASE</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.springframework/spring-webmvc -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>5.2.4.RELEASE</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.springframework/spring-test -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-test</artifactId>
<version>5.2.4.RELEASE</version>
<scope>test</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/org.springframework/spring-aop -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-aop</artifactId>
<version>5.2.4.RELEASE</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.springframework/spring -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring</artifactId>
<version>5.2.3.RELEASE</version>
<type>pom</type>
</dependency>
JVM is great！
JVM optimization
/acs/user/monitoragent/jre/bin/java -server
-Xmx128m
-Xms128m
-Xmn70m
-XX:SurvivorRatio=10
-XX:PermSize=25m
-XX:MaxPermSize=30m
-XX:+DisableExplicitGC
-XX:+UseConcMarkSweepGC
-XX:+CMSParallelRemarkEnabled
-XX:+UseCMSCompactAtFullCollection
-XX:+CMSClassUnloadingEnabled
-XX:LargePageSizeInBytes=128m
-XX:+UseFastAccessorMethods
-XX:+UseCMSInitiatingOccupancyOnly
-XX:CMSInitiatingOccupancyFraction=70
-XX:+UseParNewGC
-verbose:gc
-Xloggc:/acs/monitor/system/monitoragent/logs/gc.log
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-Duser.timezone=GMT+8
-Djava.endorsed.dirs=
-classpath /acs/user/monitoragent/lib:/acs/user/monitoragent/lib/aliyun-openservices-sls-v0.3-inner-0.1.0.jar:/acs/user/monitoragent/lib/aliyun-openservices-with-mqs.1.0.12.jar:/acs/user/monitoragent/lib/commons-beanutils-1.8.3.jar:/acs/user/monitoragent/lib/commons-codec-1.4.jar:/acs/user/monitoragent/lib/commons-collections-3.2.1.jar:/acs/user/monitoragent/lib/commons-digester-1.8.jar:/acs/user/monitoragent/lib/commons-httpclient-3.1.jar:/acs/user/monitoragent/lib/commons-lang-2.6.jar:/acs/user/monitoragent/lib/commons-lang3-3.1.jar:/acs/user/monitoragent/lib/commons-logging-1.0.4.jar:/acs/user/monitoragent/lib/commons-validator-1.4.0.jar:/acs/user/monitoragent/lib/diamond-client-3.6.7.jar:/acs/user/monitoragent/lib/diamond-utils-3.1.3.jar:/acs/user/monitoragent/lib/ezmorph-1.0.6.jar:/acs/user/monitoragent/lib/fastjson-1.2.41.jar:/acs/user/monitoragent/lib/hamcrest-core-1.1.jar:/acs/user/monitoragent/lib/httpclient-4.2.1.jar:/acs/user/monitoragent/lib/httpcore-4.2.1.jar:/acs/user/monitoragent/lib/jackson-core-lgpl-1.9.6.jar:/acs/user/monitoragent/lib/jackson-mapper-lgpl-1.9.6.jar:/acs/user/monitoragent/lib/jdom-1.1.jar:/acs/user/monitoragent/lib/json-lib-2.4-jdk15.jar:/acs/user/monitoragent/lib/junit-4.10.jar:/acs/user/monitoragent/lib/log4j-1.2.17.jar:/acs/user/monitoragent/lib/mysql-connector-java-5.1.25.jar:/acs/user/monitoragent/lib/netty-all-4.0.36.Final.jar:/acs/user/monitoragent/lib/nginx.agent.jar:/acs/user/monitoragent/lib/ons-api-1.1.5.jar:/acs/user/monitoragent/lib/ons-client-1.1.5.jar:/acs/user/monitoragent/lib/protobuf-java-2.4.1.jar:/acs/user/monitoragent/lib/rocketmq-client-3.6.4.jar:/acs/user/monitoragent/lib/rocketmq-common-3.6.4.jar:/acs/user/monitoragent/lib/rocketmq-remoting-3.6.4.jar:/acs/user/monitoragent/lib/slf4j-api-1.7.5.jar:/acs/user/monitoragent/lib/slf4j-log4j12-1.7.5.jar:/acs/user/monitoragent/lib/test.junit-4.8.1.jar:/acs/user/monitoragent/lib/test.junit.hamcrest-1.1.jar: -Dagent.home=/acs/user/monitoragent com.alibaba.ace.nginx.agent.Startup /acs/user/monitoragent/conf
More options, more KPI, more salary jobs!
Object boxing and unboxing
public static void f() {
String[] a = new String[2];
Object[] b = a;
a[0] = "hi";
b[1] = Integer.valueOf(42);
}
Return in finally
static String a() {
try {
throw new RuntimeException("a");
} catch (RuntimeException e) {
return "d";
} catch (Exception e) {
return "b";
} finally {
return "c";
}
// return "d";
}
Use ==
String s1 = new String("cccc");
String s2 = new String("cccc");
if(s1==s2){
goto hell;
}
Integer a =127;
Integer b = 127;
System.out.println(a==b);//true
Integer a1 = 128;
Integer b1 = 128;
System.out.println(a1==b1);//false
Use / as much as you can
import java.util.Scanner;
public class Exercise1 {
public static void main(String[] args){
Scanner in = new Scanner(System.in);
System.out.print("Input an integer number: ");
int n = in.nextInt();
if (n <= 0) {
System.out.print("Input a correct number.");
}
int x = 0;
while (n != 1) {
if (n % 5 == 0) {
n /= 5;
} else if (n % 3 == 0) {
n /= 3;
} else if (n % 2 == 0) {
n /= 2;
} else {
System.out.print("It is not an ugly number.");
x = 1;
break;
}
}
if (x==0)
System.out.print("It is an ugly number.");
System.out.print("\n");
}
}
Object.toString is awsome!
String[] words = { “Hello”, “World” };
System.out.println(words); //[Ljava.lang.String;@45ee12a7
Save file twice for guarantee
saveFile(fileName);
saveFile(fileName);
Sleep for further optimization
// After our customers pay the last bill,then we will comment this.
Thread.sleep(30000)；
NullPointerException is your best friend!
{
Integer n = null;
if (n == 0) {
System.out.println("n == 0");
}
}
Dreaming about generics
public class Vector<E> {
private E e = new E(); // you're dreaming
private E[] e = new E[10]; // you're dreaming
}
Try, Try, Try
public byte[] download(String url) {
HttpGet httpGet = new HttpGet(url);
try (CloseableHttpResponse response = client.execute(httpGet)) {
if (404 == response.getStatusLine().getStatusCode()) {
return null;
}
try (InputStream inputStream = response.getEntity().getContent()) {
return readInputStream(inputStream);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
httpGet = null;
}
return null;
}
Love my wife like crazy
package com.zeusro;
import java.util.Date;
public interface Wife {
public void want(Float money);
public void want(Float money,Object love);
public void want(Object love,Float money);
public void want(Object love, Float money, Date time);
}
More code lines,more money
The 40-year-old Kobe Bryant still wakes up before the sun to go to the gym at 4 a.m.
One day he asked IT engineers around him："Have you ever seen LA at 4 a.m. ?"
Go senior backend engineer : NO!
C# senior backend engineer : NO!
Kotlin senior engineer : NO!
Java senior backend engineer : YES!I am still busy on generating get and set.
import java.util.Arrays;
public class DataExample {
private final String name;
private int age;
private double score;
private String[] tags;
public DataExample(String name) {
this.name = name;
}
public String getName() {
return this.name;
}
void setAge(int age) {
this.age = age;
}
public int getAge() {
return this.age;
}
public void setScore(double score) {
this.score = score;
}
public double getScore() {
return this.score;
}
public String[] getTags() {
return this.tags;
}
public void setTags(String[] tags) {
this.tags = tags;
}
@Override public String toString() {
return "DataExample(" + this.getName() + ", " + this.getAge() + ", " + this.getScore() + ", " + Arrays.deepToString(this.getTags()) + ")";
}
protected boolean canEqual(Object other) {
return other instanceof DataExample;
}
@Override public boolean equals(Object o) {
if (o == this) return true;
if (!(o instanceof DataExample)) return false;
DataExample other = (DataExample) o;
if (!other.canEqual((Object)this)) return false;
if (this.getName() == null ? other.getName() != null : !this.getName().equals(other.getName())) return false;
if (this.getAge() != other.getAge()) return false;
if (Double.compare(this.getScore(), other.getScore()) != 0) return false;
if (!Arrays.deepEquals(this.getTags(), other.getTags())) return false;
return true;
}
@Override public int hashCode() {
final int PRIME = 59;
int result = 1;
final long temp1 = Double.doubleToLongBits(this.getScore());
result = (result*PRIME) + (this.getName() == null ? 43 : this.getName().hashCode());
result = (result*PRIME) + this.getAge();
result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));
result = (result*PRIME) + Arrays.deepHashCode(this.getTags());
return result;
}
public static class Exercise<T> {
private final String name;
private final T value;
private Exercise(String name, T value) {
this.name = name;
this.value = value;
}
public static <T> Exercise<T> of(String name, T value) {
return new Exercise<T>(name, value);
}
public String getName() {
return this.name;
}
public T getValue() {
return this.value;
}
@Override public String toString() {
return "Exercise(name=" + this.getName() + ", value=" + this.getValue() + ")";
}
protected boolean canEqual(Object other) {
return other instanceof Exercise;
}
@Override public boolean equals(Object o) {
if (o == this) return true;
if (!(o instanceof Exercise)) return false;
Exercise<?> other = (Exercise<?>) o;
if (!other.canEqual((Object)this)) return false;
if (this.getName() == null ? other.getValue() != null : !this.getName().equals(other.getName())) return false;
if (this.getValue() == null ? other.getValue() != null : !this.getValue().equals(other.getValue())) return false;
return true;
}
@Override public int hashCode() {
final int PRIME = 59;
int result = 1;
result = (result*PRIME) + (this.getName() == null ? 43 : this.getName().hashCode());
result = (result*PRIME) + (this.getValue() == null ? 43 : this.getValue().hashCode());
return result;
}
}
}
Set<Integer> s = new HashSet<>();
s.add(1);
s.add(2);
s.add(3);
s.add(4);
Thanks
- https://www.w3resource.com/java-exercises/numbers/java-number-exercise-1.php
- https://blog.csdn.net/qq_36785612/article/details/86499466
- https://blog.csdn.net/u011928958/article/details/74999256
- https://www.jianshu.com/p/bbf8c28101e9
- https://zhuanlan.zhihu.com/p/29010605
- https://en.wikipedia.org/wiki/Java_version_history