基礎知識（Integer和int的比較==）

Java會自動進行拆箱裝箱，是以int和Integer的比較是值，值相等永遠相等。（Integer和int比較時，Integer會自動拆箱）

如果是兩個Integer比較，這絕對不相等，因為比較的是兩個對象，記憶體位址都不一樣。

Integer和int比較時，Integer可能為空的情況下：

String.valueOf(foldeType).equals(x.getFoldeType())
           

空指針異常

Integer a = null;
System.out.println(a==2);
           

錯誤提示：

Exception in thread "main" java.lang.NullPointerException
	at imooccache.ImoocCache1.main(ImoocCache1.java:37)
           

在-128到127的範圍裡會利用IntegerCache緩存。

Integer b = 1026;
Integer c = 1026;
System.out.println(b==c);//false


Integer b = -128;
Integer c = -128;
System.out.println(b==c);//true


Integer b = 127;
Integer c = 127;
System.out.println(b==c);//true
           

對象裡的age是int

public static void main(String[] args) {
    int a =1026;
    Integer b = 1026;
    Man man = new Man(1026);
    System.out.println(man.getAge() == a);//true
    System.out.println(man.getAge() == b);//true
    System.out.println(a == b);//true
}
static class Man {
    private int age;
    public Man(Integer age) {
        this.age = age;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}
           

對象裡的age是Integer

public static void main(String[] args) {
    int a =1026;
    Integer b = 1026;
    Man man = new Man(1026);
    System.out.println(man.getAge() == a);//true
    System.out.println(man.getAge() == b);//false
    System.out.println(a == b);//true
}
static class Man {
    private Integer age;
    public Man(Integer age) {
        this.age = age;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
}
           

再例如：

public static void main(String[] args) {
    int a =1026;
    Integer b = 1026;
    int c = 1026;
    Integer d = 1026;
    System.out.println(a == b);//true
    System.out.println(a == c);//true
    System.out.println(a == d);//true
    System.out.println(b == c);//true
    System.out.println(b == d);//false
    System.out.println(c == d);//true
}
           

Integer的緩存區源碼：

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() {}
}