java的自动拆装箱介绍

package com.hzp.CZX;
/**
 * 测试拆装箱
 * @author 夜孤寒
 * @version 1.1.1
 */
public class TestDemo {
    /**
     * 拆装箱JDK1.5后
     */
    public static void first(){
        Integer i=7;//基本类型-->引用类型
        int j=i;//引用类型-->基本类型
        System.out.println(j);
    }
    /**
     * 拆装箱JDK1.4
     */
    public static void second(){
        Integer i=new Integer(78);
        int j=i.intValue();
        System.out.println(j);
    }
    /**
     * 测试方法
     * @param args
     */
    public static void main(String[] args) {
        first();
        second();
    }
}

package com.ygh.CZX;
/**
 * 关于java的拆装箱范围剖析
 * @author 夜孤寒
 * @version 1.1.1
 */
public class Test {
    /**
     * 以Integer类型为例
     */
    public static void first(){
        Integer i=new Integer(124);
        Integer j=new Integer(124);
        System.out.println(i==j);//false
        Integer a1=-128;
        Integer a2=-128;
        System.out.println(a1==a2);//true
        Integer b1=-129;
        Integer b2=-129;
        System.out.println(b1==b2);//false
        Integer c1=127;
        Integer c2=127;
        System.out.println(c1==c2);//true
        Integer d1=128;
        Integer d2=128;
        System.out.println(d1==d2);//false
    }
    public static void main(String[] args) {
        first();
        
    }
}

    /**
     * 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);
    }

 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() {}
    }

package com.ygh.CZX;

/**
 * 关于java的拆装箱范围剖析
 * 
 * @author 夜孤寒
 * @version 1.1.1
 */
public class Test {
    /**
     * Double
     */
    public static void first() {
        Double i1 = 100.0;
        Double i2 = 100.0;
        Double i3 = 200.0;
        Double i4 = 200.0;
        System.out.println(i1 == i2);//false
        System.out.println(i3 == i4);//false
    }
    /**
     * 测试方法
     */
    public static void main(String[] args) {
        first();
    }
}

    /**
     * Returns a {@code Double} instance representing the specified
     * {@code double} value.
     * If a new {@code Double} instance is not required, this method
     * should generally be used in preference to the constructor
     * {@link #Double(double)}, as this method is likely to yield
     * significantly better space and time performance by caching
     * frequently requested values.
     *
     * @param  d a double value.
     * @return a {@code Double} instance representing {@code d}.
     * @since  1.5
     */
    public static Double valueOf(double d) {
        return new Double(d);
    }