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"public class Test&nbs...

[单选题]

"public class Test {

    public static void main(String[] args) {
        Integer f1 = 100, f2 = 100, f3 = 150, f4 = 150;

        System.out.println(f1 == f2);
        System.out.println(f3 == f4);
    }
}"

```
true/false
```
```
true/true
```
```
fasle/ture
```

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走在修行的大街上

Integer 类型的会缓存-128~127 之间的数

private static class IntegerCache {
    static final int low = -128;
    static final int high;
    static final Integer ***[];
    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;
        *** = new Integer[(high - low) + 1];
        int j = low;
        for(int k = 0; k < ***.length; k++)
            ***[k] = new Integer(j++);
        // range [-128, 127] must be interned (JLS7 5.1.7)
        assert IntegerCache.high >= 127;
    }
    private IntegerCache() {}
}

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

发表于 2019-01-17 21:00:19 回复(0)