数组和集合的增强for

数组的增强for

@Test
public void test1(){
Integer[] integers = new Integer[5];
for(int i=0;i<integers.length;i++){
integers[i] = i;
}

for (Integer integer : integers) {
System.out.println(integer);
}
}

输出

0
1
2
3
4

对应代码的.class

@Test
public void test1() {
Integer[] integers = new Integer[5];

for(int i = 0; i < integers.length; ++i) {
integers[i] = i;
}

Integer[] var6 = integers;
int var3 = integers.length;

for(int var4 = 0; var4 < var3; ++var4) {
Integer integer = var6[var4];
System.out.println(integer);
}

}

集合的增强for

@Test
public void test1(){
ArrayList list = new ArrayList<>();
list.add(1);
list.add(11);
list.add(1111);
list.add(11111);
for (Integer integer : list) {
System.out.println(integer);
}
}

集合增强for的.class

@Test
public void test1() {
ArrayList list = new ArrayList();
list.add(1);
list.add(11);
list.add(1111);
list.add(11111);
Iterator var2 = list.iterator();

while(var2.hasNext()) {
Integer integer = (Integer)var2.next();
System.out.println(integer);
}

}

结论:

集合的增强for底层使用迭代器

数组增强for的时候改变

@Test
public void test2(){
Integer[] integers = new Integer[5];
for(int i=0;i<integers.length;i++){
integers[i] = i;
}

for (Integer integer : integers) {
if(integer==2){
integer=2222222;
}
}
for (Integer integer : integers) {
System.out.println(integer);
}
}

数组增强for改变时候的class

@Test
public void test2() {
Integer[] integers = new Integer[5];

for(int i = 0; i < integers.length; ++i) {
integers[i] = i;
}

Integer[] var6 = integers;
int var3 = integers.length;

int var4;
Integer integer;
for(var4 = 0; var4 < var3; ++var4) {
integer = var6[var4];
if (integer == 2) {
integer = 2222222;
}
}

var6 = integers;
var3 = integers.length;

for(var4 = 0; var4 < var3; ++var4) {
integer = var6[var4];
System.out.println(integer);
}

}

集合增强for的时候改变

@Test
public void test3(){
ArrayList list = new ArrayList<>();
list.add(1);
list.add(11);
list.add(111);
list.add(1111);
for (Integer integer : list) {
if(integer==11){
integer = 0;
}
}

for (Integer integer : list) {
System.out.println(integer);
}
}

结果

1
11
111
1111

增强for改变的.class文件

@Test
public void test3() {
ArrayList list = new ArrayList();
list.add(1);
list.add(11);
list.add(111);
list.add(1111);
Iterator var2 = list.iterator();

Integer integer;
while(var2.hasNext()) {
integer = (Integer)var2.next();
if (integer == 11) {
integer = 0;
}
}

var2 = list.iterator();

while(var2.hasNext()) {
integer = (Integer)var2.next();
System.out.println(integer);
}

}