Does anyone have any clever memory-saving tips to share?

The app I've been working on has been bumping up against the amount of memory we have, so I've come up with a few strategies that have helped alleviate the problem. Here they are...

1) Pack booleans into an int.

One of our classes has a bunch of boolean fields. Each boolean field is inefficiently stored in a 32-bit int. Now we just have one int field, which can hold all of the booleans.

The code looks like this...

<pre>
public Item {
// member variable for holding booleans
public int itemBooleans;

// utility for setting boolean values in the int
private void setItemBoolean(int pos, boolean val) {
int powerOfTwo = 1 << pos;
if (val)
this.itemBooleans |= powerOfTwo;
else
this.itemBooleans &= (Integer.MAX_VALUE-powerOfTwo);
}

// utility method for extracting boolean values out of the int
private boolean getItemBoolean(int pos) {
int powerOfTwo = 1 << pos;
return ((this.itemBooleans & powerOfTwo) != 0);
}

public void setIsRound(boolean b) {
setItemBoolean(0, b);
}

public boolean getIsRound() {
return getItemBoolean(0);
}

public void setIsSquare(boolean b) {
setItemBoolean(1, b);
}

public boolean getIsSquare() {
return getItemBoolean(1);
}
}
</pre>


2) Pack Dates into ints.

My first observation was that it's wasteful to store a Date object when all you really need to do is store the long value that the Date wraps. The class's API should use Date objects, but internally the Dates should be stored as longs.

My second observation is that if you only need accuracy to the nearest second, instead of to the nearest millisecond, then you don't even need a long. An int works just fine.

The code looks like this:

<pre>
import java.util.Date;

public abstract class DateUtils {

public static Date intToDate(int time) {
return (time != 0) ? new Date((long)time * 1000) : null;
}

public static int dateToInt(Date date) {
return (date != null) ? ((int) (date.getTime() / 1000)) : 0;
}
}


public class Item {
// member varibale that holds a date value
int creationDate;

public void setCreationDate(Date creationDate) {
this.creationDate = DateUtils.dateToInt(creationDate);
}

public Date getCreationDate() {
return DateUtils.intToDate(this.creationDate);
}
}
</pre>