Java基础笔记 – 增强的for循环For each循环 自动装箱拆箱 可变参数

for(type element : array){
    …
System.out.println(element);
    …
}

public static void main(String[] args) {
    List<String> arrayList = new ArrayList<String>();
    arrayList.add("a");
    arrayList.add("b");
    arrayList.add("c");

    //普通的循环方式
    for(int i=0; i<arrayList.size(); i++){
        System.out.println(arrayList.get(i));
    }

    //使用For each循环
    for(String element : arrayList){
        System.out.println(element);
    }
}

int[][] array = {{1,2,3},{1,2}};
for(int[] row : array){
    for(int element : row){
        System.out.println(element);
    }
}

//普通的循环方式
for(int i=0; i<arrayList.size(); i++){
    System.out.println(arrayList.get(i));
}

//迭代循环
for(Iterator<String> iter = arrayList.iterator(); iter.hasNext();){
    System.out.println(iter.next());
}

//使用For each循环
for(String element : arrayList){
    System.out.println(element);
}

//使用For each循环
int i = 0;
for(String element : arrayList){
    System.out.println(i + element);
    i++;
}

//自动装箱
Collection<Integer> c = new ArrayList<Integer>();
c.add(1);
c.add(2);
c.add(3);

//自动拆箱
for(Integer integer : c){
    System.out.println(integer);
}

public static Integer valueOf(int i) {
        if(i >= -128 && i <= IntegerCache.high)
            return IntegerCache.cache[i + 128];
        else
            return new Integer(i);
    }

private static class IntegerCache {
        static final int high;
        static final Integer cache[];

        static {
            final int low = -128;

            // high value may be configured by property
            int h = 127;
            if (integerCacheHighPropValue != null) {
                // Use Long.decode here to avoid invoking methods that
                // require Integer's autoboxing cache to be initialized
                int i = Long.decode(integerCacheHighPropValue).intValue();
                i = Math.max(i, 127);
                // Maximum array size is Integer.MAX_VALUE
                h = Math.min(i, Integer.MAX_VALUE - -low);
            }
            high = h;

            cache = new Integer[(high - low) + 1];
            int j = low;
            for(int k = 0; k < cache.length; k++)
                cache[k] = new Integer(j++);
        }

        private IntegerCache() {}
    }

Integer m = 127;
Integer n = 127;
System.out.println(m == n);

Integer m = 128;
Integer n = 128;
System.out.println(m == n);

public static int add(int... arrays){
    int sum = 0;
    for(Integer integer : arrays){
        sum += integer;
    }
    return sum;
}

//传递数组
add(new int[]{1,2,3});
//传递参数
add(1,2,3);