如何在Java中找到最大内存,可用内存和总内存?

2021年3月16日12:30:43 发表评论 719 次浏览

尽管Java提供了自动垃圾收集

, 有时你会想知道对象堆有多大, 还剩下多少。该信息可用于检查代码的效率, 并大约检查可实例化某种类型的更多对象。要获得这些值, 我们使用

totalMemory()

freeMemory

方法。

众所周知, Java的垃圾回收器会定期运行以回收未使用的对象。我们可以通过调用

GC()

方法。尝试拨打电话是一件好事

GC()

然后打电话

freeMemory()

.

方法:

void gc():

运行垃圾收集器。调用此方法表明, Java虚拟机将努力扩展回收未使用的对象, 以使它们当前占用的内存可用于快速重用。当控制从方法调用返回时, 虚拟机将尽最大努力回收所有丢弃的对象。

语法如下:

public void gc()
Returns: NA.
Exception: NA.

long freeMemory():

此方法返回Java虚拟机中的可用内存量。调用gc方法可能会增加freeMemory返回的值。

语法如下:

public long freeMemory()
Returns: an approximation to the total
amount of memory currently available for
future allocated objects, measured in bytes.
Exception: NA.

long totalMemory():

此方法返回Java虚拟机中的内存总量。此方法返回的值可能会随时间变化, 具体取决于主机环境。

语法如下:

public long totalMemory()
Returns: the total amount of memory 
currently available for current and future 
objects, measured in bytes.
Exception: NA.
// Java code illustrating gc(), freeMemory()
// and totalMemory() methods
class memoryDemo
{
     public static void main(String arg[])
     {
         Runtime gfg = Runtime.getRuntime();
         long memory1, memory2;
         Integer integer[] = new Integer[ 1000 ];
  
         // checking the total memeory
         System.out.println( "Total memory is: "
                            + gfg.totalMemory());
  
         // checking free memory
         memory1 = gfg.freeMemory();
         System.out.println( "Initial free memory: "
                                       + memory1);
  
         // calling the garbage collector on demand
         gfg.gc();
  
         memory1 = gfg.freeMemory();
  
         System.out.println( "Free memory after garbage "
                            + "collection: " + memory1);
  
         // allocating integers
         for ( int i = 0 ; i < 1000 ; i++)
             integer[i] = new Integer(i);
  
         memory2 = gfg.freeMemory();
         System.out.println( "Free memory after allocation: "
                            + memory2);
  
         System.out.println( "Memeory used by allocation: " +
                                     (memory1 - memory2));
  
         // discard integers
         for ( int i = 0 ; i < 1000 ; i++)
             integer[i] = null ;
  
         gfg.gc();
  
         memory2 = gfg.freeMemory();
         System.out.println( "Free memeory after  "
             + "collecting discarded Integers: " + memory2);
     }
}

输出如下:

Total memory is: 128974848
Initial free memory: 126929976
Free memory after garbage collection: 128632384
Free memory after allocation: 127950744
Memory used by allocation: 681640
Free memory after collecting discarded Integers: 128643696

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木子山

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