关于Interger和int

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我是靠谱客的博主会撒娇缘分，这篇文章主要介绍关于Interger和int，现在分享给大家，希望可以做个参考。

Java是一个近乎纯洁的面向对象编程语言，但是为了编程的方便还是引入了基本数据类型，但是为了能够将这些基本数据类型当成对象操作，Java为每一个基本数据类型都引入了对应的包装类型（wrapper class），int的包装类就是Integer，从Java 5开始引入了自动装箱/拆箱机制，使得二者可以相互转换。
Java 为每个原始类型提供了包装类型。
下面用代码说明一些问题：

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public class test {
public static void main(String[] args) {
Integer a = new Integer(6);
Integer b = 6;
int c = 6;
System.out.println(a == b);//ab虽然都是Interger 但是ab没有引用同意对象
System.out.println(a == c);//a自动拆箱成int类型再和c比较
}
}

答案是false和true

但是！！！

public class test {
public static void main(String[] args) {

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Integer f1 = 100, f2 = 100, f3 = 130, f4 = 130;
System.out.println(f1 == f2);
System.out.println(f3 == f4);
}

}
结果会是什么呢？你会觉得他们都是true 因为都是引用一个对象对吧？
但是答案却是true和false 为什么？
装箱的本质是什么呢？当我们给一个Integer对象赋一个int值的时候，会调用Integer类的静态方法valueOf，如果看看valueOf的源代码就知道发生了什么。

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public static Integer valueOf(int i) {
if (i >= IntegerCache.low && i <= IntegerCache.high)
return IntegerCache.cache[i + (-IntegerCache.low)];
return new Integer(i);
}

IntegerCache是Integer的内部类，其代码如下所示：

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/**
* Cache to support the object identity semantics of autoboxing for values between
* -128 and 127 (inclusive) as required by JLS.
*
* The cache is initialized on first usage.
The size of the cache
* may be controlled by the {@code -XX:AutoBoxCacheMax=<size>} option.
* During VM initialization, java.lang.Integer.IntegerCache.high property
* may be set and saved in the private system properties in the
* sun.misc.VM class.
*/
private static class IntegerCache {
static final int low = -128;
static final int high;
static final Integer cache[];
static {
// high value may be configured by property
int h = 127;
String integerCacheHighPropValue =
sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
if (integerCacheHighPropValue != null) {
try {
int i = parseInt(integerCacheHighPropValue);
i = Math.max(i, 127);
// Maximum array size is Integer.MAX_VALUE
h = Math.min(i, Integer.MAX_VALUE - (-low) -1);
} catch( NumberFormatException nfe) {
// If the property cannot be parsed into an int, ignore it.
}
}
high = h;
cache = new Integer[(high - low) + 1];
int j = low;
for(int k = 0; k < cache.length; k++)
cache[k] = new Integer(j++);
// range [-128, 127] must be interned (JLS7 5.1.7)
assert IntegerCache.high >= 127;
}
private IntegerCache() {}
}

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/**
* Cache to support the object identity semantics of autoboxing for values between
* -128 and 127 (inclusive) as required by JLS.
*
* The cache is initialized on first usage.
The size of the cache
* may be controlled by the {@code -XX:AutoBoxCacheMax=<size>} option.
* During VM initialization, java.lang.Integer.IntegerCache.high property
* may be set and saved in the private system properties in the
* sun.misc.VM class.
*/
private static class IntegerCache {
static final int low = -128;
static final int high;
static final Integer cache[];
static {
// high value may be configured by property
int h = 127;
String integerCacheHighPropValue =
sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
if (integerCacheHighPropValue != null) {
try {
int i = parseInt(integerCacheHighPropValue);
i = Math.max(i, 127);
// Maximum array size is Integer.MAX_VALUE
h = Math.min(i, Integer.MAX_VALUE - (-low) -1);
} catch( NumberFormatException nfe) {
// If the property cannot be parsed into an int, ignore it.
}
}
high = h;
cache = new Integer[(high - low) + 1];
int j = low;
for(int k = 0; k < cache.length; k++)
cache[k] = new Integer(j++);
// range [-128, 127] must be interned (JLS7 5.1.7)
assert IntegerCache.high >= 127;
}
private IntegerCache() {}
}