分支数 小于三时,else if 效率更高 等于三时,效率近乎相同 大于三时,switch case效率更高
package Action;
public class HelloWorld {
static int count=10000000;
public static void main(String[] args) {
if_test();
System.gc();//清理一下
switch_test();
}
public static void if_test() {
long start = System.currentTimeMillis();
for (int i = 0; i <count; i++) {
if(i==(10000000-1)) {
System.out.println("if判断一千万次");
}
}
long end = System.currentTimeMillis();
System.out.println("if判断一千万次"+(end-start)+"毫秒");
}
public static void switch_test() {
long start = System.currentTimeMillis();
for (int i = 0; i <count; i++) {
switch(i) {
case 10000000-1:System.out.println("switch判断一千万次");break;
}
}
long end = System.currentTimeMillis();
System.out.println("switch判断一千万次"+(end-start)+"毫秒");
}
}
区别还算明显吧,量少,可以用一亿试试。
package Action;
public class HelloWorld {
static int count=100000000;
public static void main(String[] args) {
if_test();
System.gc();//清理一下
switch_test();
}
public static void if_test() {
long start = System.currentTimeMillis();
for (int i = 0; i <count; i++) {
if(i==(100000000-1)) {
System.out.println("if判断一亿次");
}
}
long end = System.currentTimeMillis();
System.out.println("if判断一亿次"+(end-start)+"毫秒");
}
public static void switch_test() {
long start = System.currentTimeMillis();
for (int i = 0; i <count; i++) {
switch(i) {
case 100000000-1:System.out.println("switch判断一亿次");break;
}
}
long end = System.currentTimeMillis();
System.out.println("switch判断一亿次"+(end-start)+"毫秒");
}
}
这就很明显了。
package Action;
public class HelloWorld {
static int count=10000000;
public static void main(String[] args) {
switch_test();
if_test();
}
public static void if_test() {
long start = System.currentTimeMillis();
for (int i = 0; i <count; i++) {
if(i==(10000000-1)) {
System.out.println("if判断一千万次");
}else if(i==-1) {
}else if(i==-2){
}
}
long end = System.currentTimeMillis();
System.out.println("if判断一千万次"+(end-start)+"毫秒");
}
public static void switch_test() {
long start = System.currentTimeMillis();
for (int i = 0; i <count; i++) {
switch(i) {
case 10000000-1:System.out.println("switch判断一千万次");break;
case -1:break;
case -2:break;
}
}
long end = System.currentTimeMillis();
System.out.println("switch判断一千万次"+(end-start)+"毫秒");
}
}
三个的时候其实还是if快一些。
package Action;
public class HelloWorld {
static int count=10000000;
public static void main(String[] args) {
if_test();
System.gc();
switch_test();
}
public static void if_test() {
long start = System.currentTimeMillis();
for (int i = 0; i <count; i++) {
if(i==(10000000-1)) {
System.out.println("if判断一千万次");
}else if(i==-1) {
}else if(i==-2){
}else if(i==-3){
}else if(i==-4){
}else if(i==-5){
}else if(i==-6){
}else if(i==-7){
}else if(i==-8){
}else if(i==-9){
}else if(i==-10){
}
}
long end = System.currentTimeMillis();
System.out.println("if判断一千万次"+(end-start)+"毫秒");
}
public static void switch_test() {
long start = System.currentTimeMillis();
for (int i = 0; i <count; i++) {
switch(i) {
case 10000000-1:System.out.println("switch判断一千万次");break;
case -1:break;
case -2:break;
case -3:break;
case -4:break;
case -5:break;
case -6:break;
case -7:break;
case -8:break;
case -9:break;
case -10:break;
}
}
long end = System.currentTimeMillis();
System.out.println("switch判断一千万次"+(end-start)+"毫秒");
}
}
这回效果还是比较明显的,用一亿再试试:
这就更明显了。
希望能对大家有所帮助。