Anton Saburov Студенческий отдел кадров

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Настройки java

Системные настройки

Environment Variables
JAVA_HOME = C:\Program Files\Java\jdk1.5.0
ANT_HOME = D:\apps\ant
PATH = %ANT_HOME%\bin;%JAVA_HOME%\bin;%PATH%

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String

Вывод с параметрами

char x = 'x';
int cast = (int)x;
int codePoint = String.valueOf(x).codePointAt(0);
char again = (char)codePoint;
System.out.printf("x = %s cast = %d codePoint = %d again = %s%n",
x, cast, codePoint, again);

if ( s.equals ( "abc" ) ) echo ( "matched" );
Java Glossary | String

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Джавские фишечки

\n - new line "\n"
\t - табулятор "\t"
\u2192, \u204B - знаки вопроса ? "\u2192" etc
Escape Sequences

toString

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.
The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

getClass().getName() + '@' + Integer.toHexString(hashCode())

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Loop time

2.21 ГГц, 1.00 ГБ ОЗУ


100000000
19:50:41
19:50:48


1000000000
19:51:33
19:52:37


10000000000
19:54:01
20:04:41

package loop_test;

import java.util.Calendar;

import java.text.SimpleDateFormat;


public class loop_test {
public loop_test() {
}

//public static final String DATE_FORMAT_NOW = "yyyy-MM-dd HH:mm:ss";
//public static final String DATE_FORMAT_NOW = "dd-MMMM-yyyy HH:mm:ss";
public static final String DATE_FORMAT_NOW = "HH:mm:ss";

public static void main(String[] args) {
loop_test lt = new loop_test();
Long j = 0L;
Long n = 10000000000L;
System.out.println(n);
System.out.println(lt.now());
for (Long i = 0L; i < n; i++) {
j++;
Math.sqrt(j);
}
System.out.println(lt.now());
}


public String now() {
Calendar cal = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT_NOW);
return sdf.format(cal.getTime());
}

}

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java.lang.OutOfMemoryError

JDeveloper running a simple Java class threw:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space

This is a standard java exception treated by adding parameters to java in command line as the default parameters are -Xms32m -Xmx128m.

This case solution was found in a discussion about analogous exception for embedded OC4J.

Just edit Run Configuration adding -Xms512m -Xmx1024m (for example) in Project Properties... | Run/Debug | Edit... | Java Options edit bar

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