Integer and = = compare

Project scenario ：

Tips ： Here is a brief introduction to the background of the project ：
a bittler loser, No time-consuming on the problem
By the way, there is another problem here besides the seemingly one, that is integer The way of comparison :

Problem description

Tips ： The problems encountered in the project are described here ：

My way is ： This way is ： It turned out to be wrong ：

Integer a1 = new Integer(1);
	System.out.println(a1.toString().equals("1")); // String comparison 
	System.out.println(a1.equals("1"));  //inteer  Comparison ：

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Cause analysis ：

Tips ： Fill in the analysis of the problem here ：
public boolean equals(Object obj) {
if (obj instanceof Integer) {
return value == ((Integer)obj).intValue();
}
return false;
}
You can see whether the object of comparison is Integer Type of , If yes, turn to int The basic type is reused == Compare , The comparison is the value . So something special .
The essence of the source code is that it cannot be converted into int Type, otherwise it returns false. Of .
however

Solution ：

Tips ： Fill in the specific solution to the problem here ：

Check the information to know Integer There is a cache array , namely -128<=value<=127, Get from the cache array Integer object . For ,q and w Both exceed the cached value , So it's all new New object of , therefore It doesn't match . So it's not difficult for us to understand ,Integer Of “” The method is to compare addresses . and Integer Of equals Methods will not have these problems , It's a direct literal comparison .

Therefore use Integer When making a comparison , Whether the distinction of exceeds the area of the cache array .
Large numbers are used for comparison integer, Small data comparison ==.