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java中double強(qiáng)制轉(zhuǎn)換int引發(fā)的OOM問(wèn)題記錄

更新時(shí)間：2024年10月23日 09:45:38 作者：冷雨夜中漫步

這篇文章主要介紹了java中double強(qiáng)制轉(zhuǎn)換int引發(fā)的OOM問(wèn)題記錄,本文給大家分享問(wèn)題排查過(guò)程,感興趣的朋友跟隨小編一起看看吧

問(wèn)題代碼

最近出現(xiàn)了一次OOM問(wèn)題，問(wèn)題代碼如下

public void prcess(double total, int step) {
	int num = (int) Math.floor(total / step);
	while (num-- > 0) {
		doSomething(); // 普通方法，占用內(nèi)存不大
	}
}

根據(jù)單步步長(zhǎng)step將total值劃分后，然后進(jìn)行處理。然后日志中發(fā)現(xiàn)堆棧在doSomething()時(shí)報(bào)錯(cuò)OOM，拋出java.lang.OutOfMemoryError。確認(rèn)過(guò)doSomething()方法不會(huì)占用過(guò)大的內(nèi)存，那為何會(huì)發(fā)生問(wèn)題？

排查過(guò)程

懷疑num過(guò)大導(dǎo)致，查看入?yún)otal為合理值，但是step是取配置值，配置未配置時(shí)默認(rèn)為0，則問(wèn)題代碼為int num = (int) Math.floor(total / step);,這里step為0，Math.floor(total / step) = Infinity，強(qiáng)制轉(zhuǎn)為int后得到值為2147483647。一直在處理此處的邏輯導(dǎo)致內(nèi)存增長(zhǎng)，進(jìn)而發(fā)生OOM

double特殊值與強(qiáng)制轉(zhuǎn)換

java語(yǔ)言中浮點(diǎn)運(yùn)算存在兩個(gè)值：NaN與Infinity

NaN

Not-a-Number，非數(shù)字值，數(shù)學(xué)上0/0是無(wú)意義的，java在浮點(diǎn)運(yùn)算中實(shí)現(xiàn)了NaN，定義為0.0/0.0。NaN有如下幾個(gè)特點(diǎn)：

NaN與任何數(shù)字都不相等，NaN與其本身也不相等

System.out.println(Double.NaN == Double.NaN); // false
System.out.println(Double.NaN == 0.0/0.0); // false
System.out.println(Double.NaN == 0.0); // false

使用Double.isNaN或Float.isNaN確認(rèn)是否為NaN

System.out.println(Double.isNaN(0.0/0.0));  // true
System.out.println(Float.isNaN(0.0f/0.0f));  // true

NaN與任何數(shù)字比較都是false

System.out.println(Double.NaN > 0.0); // false
System.out.println(Double.NaN < 0.0); // false

Infinity

無(wú)限，分為正無(wú)限與負(fù)限小，定義為一個(gè)非0數(shù)字除以0。

有如下幾個(gè)特點(diǎn)：

正無(wú)限與負(fù)無(wú)限定義

public static final double POSITIVE_INFINITY = 1.0 / 0.0;
public static final double NEGATIVE_INFINITY = -1.0 / 0.0;

無(wú)限與任何非無(wú)限非0數(shù)字運(yùn)算仍為無(wú)限

System.out.println(Double.POSITIVE_INFINITY + Double.MAX_VALUE); // Infinity
System.out.println(Double.POSITIVE_INFINITY - Double.MAX_VALUE); // Infinity
System.out.println(Double.POSITIVE_INFINITY * Double.MAX_VALUE); // Infinity
System.out.println(Double.POSITIVE_INFINITY / Double.MAX_VALUE); // Infinity
System.out.println(Double.NEGATIVE_INFINITY + Double.MIN_VALUE); // -Infinity
System.out.println(Double.NEGATIVE_INFINITY - Double.MIN_VALUE); // -Infinity
System.out.println(Double.NEGATIVE_INFINITY * Double.MIN_VALUE); // -Infinity
System.out.println(Double.NEGATIVE_INFINITY / Double.MIN_VALUE); // -Infinity

無(wú)限與0運(yùn)算為無(wú)限或NaN

System.out.println(Double.POSITIVE_INFINITY / 0); // Infinity
System.out.println(Double.POSITIVE_INFINITY * 0); // NaN
System.out.println(Double.NEGATIVE_INFINITY / 0); // -Infinity
System.out.println(Double.NEGATIVE_INFINITY * 0); // NaN

負(fù)無(wú)限與正無(wú)限運(yùn)算為無(wú)限或NaN

System.out.println(Double.POSITIVE_INFINITY + Double.NEGATIVE_INFINITY); // NaN
System.out.println(Double.POSITIVE_INFINITY - Double.NEGATIVE_INFINITY); // Infinity
System.out.println(Double.NEGATIVE_INFINITY + Double.POSITIVE_INFINITY); // NaN
System.out.println(Double.NEGATIVE_INFINITY - Double.POSITIVE_INFINITY); // -Infinity
System.out.println(Double.POSITIVE_INFINITY * Double.NEGATIVE_INFINITY); // -Infinity
System.out.println(Double.POSITIVE_INFINITY / Double.NEGATIVE_INFINITY); // NaN
System.out.println(Double.NEGATIVE_INFINITY * Double.POSITIVE_INFINITY); // -Infinity
System.out.println(Double.NEGATIVE_INFINITY / Double.POSITIVE_INFINITY); // NaN

無(wú)限強(qiáng)制轉(zhuǎn)換為整形會(huì)有精度丟失

System.out.println((int)Double.POSITIVE_INFINITY); // Integer.MAX_VALUE
System.out.println((int)Double.NEGATIVE_INFINITY); // Integer.MIN_VALUE
System.out.println((long) Double.POSITIVE_INFINITY); // Long.MAX_VALUE
System.out.println((long)Double.NEGATIVE_INFINITY); // Long.MIN_VALUE

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