- int与Integer比较，会经历自动拆箱的过程
- 得到一个Integer由两种方式：一种是例如new Integer(123);一种是例如Integer a=123，会调用Integer.valueOf(123)方法。
- new出来的对象都是在堆上分配内存，Integer.valueOf()方法源码如下
/**
* Returns an {@code Integer} instance representing the specified
* {@code int} value. If a new {@code Integer} instance is not
* required, this method should generally be used in preference to
* the constructor {@link #Integer(int)}, as this method is likely
* to yield significantly better space and time performance by
* caching frequently requested values.
*
* This method will always cache values in the range -128 to 127,
* inclusive, and may cache other values outside of this range.
*
* @param i an {@code int} value.
* @return an {@code Integer} instance representing {@code i}.
* @since 1.5
*/
public static Integer valueOf(int i) {
if (i >= IntegerCache.low && i <= IntegerCache.high)
return IntegerCache.cache[i + (-IntegerCache.low)];
return new Integer(i);
}
-
Object类有13个方法
Object类的13个方法
其中hashCode()，equals(Object)，clone()，toString()，finalize()方法不是final的，可以由子类重写。其中equals(Object)，toString()，finalize()方法不是native的，源码如下。
public boolean equals(Object obj) {
return (this == obj);
}
public String toString() {
return getClass().getName() + "@" + Integer.toHexString(hashCode());
}
protected void finalize() throws Throwable { }
- Integer类重写了Object类的方法，包括toString()，hashCode()，equals(Object)。
public String toString() {
return toString(value);
}
public static String toString(int i) {
if (i == Integer.MIN_VALUE)
return "-2147483648";
int size = (i < 0) ? stringSize(-i) + 1 : stringSize(i);
char[] buf = new char[size];
getChars(i, size, buf);
return new String(buf, true);
}
public int hashCode() {
return Integer.hashCode(value);
}
public static int hashCode(int value) {
return value;
}
public boolean equals(Object obj) {
if (obj instanceof Integer) {
return value == ((Integer)obj).intValue();
}
return false;
}
而且Integer类implements Comparable<Integer>，实现了compareTo(Integer)和compare(int,int)方法
public int compareTo(Integer anotherInteger) {
return compare(this.value, anotherInteger.value);
}
public static int compare(int x, int y) {
return (x < y) ? -1 : ((x == y) ? 0 : 1);
}
有以下测试代码
Integer a=new Integer(1);
Integer b=new Integer(1);
System.out.println(a==b);//false
System.out.println(a.equals(b));//true
System.out.println(a.hashCode()==b.hashCode());//true
System.out.println(a.compareTo(b)==0);//true
