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看完这些 Java 代码优秀案例，一定对你有提升！
（给ImportNew加星标，提高Java技能）
作者：泥瓦匠BYsocket
慎用异常
@Test
public void test11() {
long start = System.currentTimeMillis();
int a = 0;
for(int i=0;i<1000000000;i++){
try {
a++;
}catch (Exception e){
e.printStackTrace();
}
}
long useTime = System.currentTimeMillis()-start;
System.out.println("useTime:"+useTime);
} useTime:10@Test
public void test(){
long start = System.currentTimeMillis();
int a = 0;
try {
for (int i=0;i<1000000000;i++){
a++;
}
}catch (Exception e){
e.printStackTrace();
}
long useTime = System.currentTimeMillis()-start;
System.out.println(useTime);
}useTime:6使用局部变量
@Test
public void test11() {
long start = System.currentTimeMillis();
int a = 0;
for(int i=0;i<1000000000;i++){
a++;
}
long useTime = System.currentTimeMillis()-start;
System.out.println("useTime:"+useTime);
}useTime:5static int aa = 0;
@Test
public void test(){
long start = System.currentTimeMillis();
for (int i=0;i<1000000000;i++){
aa++;
}
long useTime = System.currentTimeMillis()-start;
System.out.println("useTime:"+useTime);
}useTime:94位运算代替乘除法
@Test
public void test11() {
long start = System.currentTimeMillis();
int a = 0;
for(int i=0;i<1000000000;i++){
a*=2;
a/=2;
}
long useTime = System.currentTimeMillis()-start;
System.out.println("useTime:"+useTime);
}运行结果：
useTime:1451将循环体中的乘除运算改为等价的位运算，代码如下：
@Test
public void test(){
long start = System.currentTimeMillis();
int aa = 0;
for (int i=0;i<1000000000;i++){
aa<<=1;
aa>>=1;
}
long useTime = System.currentTimeMillis()-start;
System.out.println("useTime:"+useTime);
}useTime:10提取表达式
@Test
public void testExpression(){
long start = System.currentTimeMillis();
double d = Math.random();
double a = Math.random();
double b = Math.random();
double e = Math.random();
double x,y;
for(int i=0;i<10000000;i++){
x = d*a*b/3*4*a;
y = e*a*b/3*4*a;
}
long useTime = System.currentTimeMillis()-start;
System.out.println("useTime:"+useTime);
}useTime:21@Test
public void testExpression99(){
long start = System.currentTimeMillis();
double d = Math.random();
double a = Math.random();
double b = Math.random();
double e = Math.random();
double p,x,y;
for(int i=0;i<10000000;i++){
p = a*b/3*4*a;
x = d*p;
y = e*p;
}
long useTime = System.currentTimeMillis()-start;
System.out.println("useTime:"+useTime);
}useTime:11for(int i=0;i<100000;i++){
x[i] = Math.PI*Math.sin(y)*i;
}//提取复杂，固定结果的业务逻辑处理到循环体外
double p = Math.PI*Math.sin(y);
for(int i=0;i<100000;i++){
x[i] = p*i;
}使用arrayCopy()
/**
* @param src the source array.
* @param srcPos starting position in the source array.
* @param dest the destination array.
* @param destPos starting position in the destination data.
* @param length the number of array elements to be copied.
* @exception IndexOutOfBoundsException if copying would cause
* access of data outside array bounds.
* @exception ArrayStoreException if an element in the <code>src</code>
* array could not be stored into the <code>dest</code> array
* because of a type mismatch.
* @exception NullPointerException if either <code>src</code> or
* <code>dest</code> is <code>null</code>.
*/
public static native void arraycopy(Object src, int srcPos,
Object dest, int destPos,
int length)@Test
public void testArrayCopy(){
int size = 100000;
int[] array = new int[size];
int[] arraydest = new int[size];
for(int i=0;i<array.length;i++){
array[i] = i;
}
long start = System.currentTimeMillis();
for (int k=0;k<1000;k++){
//进行复制
System.arraycopy(array,0,arraydest,0,size);
}
long useTime = System.currentTimeMillis()-start;
System.out.println("useTime:"+useTime);
}useTime:59@Test
public void testArrayCopy99(){
int size = 100000;
int[] array = new int[size];
int[] arraydest = new int[size];
for(int i=0;i<array.length;i++){
array[i] = i;
}
long start = System.currentTimeMillis();
for (int k=0;k<1000;k++){
for(int i=0;i<size;i++){
arraydest[i] = array[i];
}
}
long useTime = System.currentTimeMillis()-start;
System.out.println("useTime:"+useTime);
}useTime:102使用Buffer进行I/O操作
使用基于InpuStream和OutputStream的方式； 使用Writer和Reader;
@Test
public void testOutAndInputStream(){
try {
DataOutputStream dataOutputStream = new DataOutputStream(new FileOutputStream("/IdeaProjects/client2/src/test/java/com/client2/cnblogtest/teststream.txt"));
long start = System.currentTimeMillis();
for(int i=0;i<10000;i++){
dataOutputStream.writeBytes(Objects.toString(i)+"\r\n");
}
dataOutputStream.close();
long useTime = System.currentTimeMillis()-start;
System.out.println("写入数据--useTime:"+useTime);
//开始读取数据
long startInput = System.currentTimeMillis();
DataInputStream dataInputStream = new DataInputStream(new FileInputStream("/IdeaProjects/client2/src/test/java/com/client2/cnblogtest/teststream.txt"));
while (dataInputStream.readLine() != null){
}
dataInputStream.close();
long useTimeInput = System.currentTimeMillis()-startInput;
System.out.println("读取数据--useTimeInput:"+useTimeInput);
}catch (Exception e){
e.printStackTrace();
}
}运行结果：
写入数据--useTime:660
读取数据--useTimeInput:274@Test
public void testBufferedStream(){
try {
DataOutputStream dataOutputStream = new DataOutputStream(
new BufferedOutputStream(new FileOutputStream("/IdeaProjects/client2/src/test/java/com/client2/cnblogtest/teststream.txt")));
long start = System.currentTimeMillis();
for(int i=0;i<10000;i++){
dataOutputStream.writeBytes(Objects.toString(i)+"\r\n");
}
dataOutputStream.close();
long useTime = System.currentTimeMillis()-start;
System.out.println("写入数据--useTime:"+useTime);
//开始读取数据
long startInput = System.currentTimeMillis();
DataInputStream dataInputStream = new DataInputStream(
new BufferedInputStream(new FileInputStream("/IdeaProjects/client2/src/test/java/com/client2/cnblogtest/teststream.txt")));
while (dataInputStream.readLine() != null){
}
dataInputStream.close();
long useTimeInput = System.currentTimeMillis()-startInput;
System.out.println("读取数据--useTimeInput:"+useTimeInput);
}catch (Exception e){
e.printStackTrace();
}
} 写入数据--useTime:22
读取数据--useTimeInput:12@Test
public void testWriterAndReader(){
try {
long start = System.currentTimeMillis();
FileWriter fileWriter = new FileWriter("/IdeaProjects/client2/src/test/java/com/client2/cnblogtest/teststream.txt");
for (int i=0;i<100000;i++){
fileWriter.write(Objects.toString(i)+"\r\n");
}
fileWriter.close();
long useTime = System.currentTimeMillis()-start;
System.out.println("写入数据--useTime:"+useTime);
//开始读取数据
long startReader = System.currentTimeMillis();
FileReader fileReader = new FileReader("/IdeaProjects/client2/src/test/java/com/client2/cnblogtest/teststream.txt");
while (fileReader.read() != -1){
}
fileReader.close();
long useTimeInput = System.currentTimeMillis()-startReader;
System.out.println("读取数据--useTimeInput:"+useTimeInput);
}catch (Exception e){
e.printStackTrace();
}
}写入数据--useTime:221
读取数据--useTimeInput:147@Test
public void testBufferedWriterAndReader(){
try {
long start = System.currentTimeMillis();
BufferedWriter fileWriter = new BufferedWriter(
new FileWriter("/IdeaProjects/client2/src/test/java/com/client2/cnblogtest/teststream.txt"));
for (int i=0;i<100000;i++){
fileWriter.write(Objects.toString(i)+"\r\n");
}
fileWriter.close();
long useTime = System.currentTimeMillis()-start;
System.out.println("写入数据--useTime:"+useTime);
//开始读取数据
long startReader = System.currentTimeMillis();
BufferedReader fileReader = new BufferedReader(
new FileReader("/IdeaProjects/client2/src/test/java/com/client2/cnblogtest/teststream.txt"));
while (fileReader.read() != -1){
}
fileReader.close();
long useTimeInput = System.currentTimeMillis()-startReader;
System.out.println("读取数据--useTimeInput:"+useTimeInput);
}catch (Exception e){
e.printStackTrace();
}
}写入数据--useTime:157
读取数据--useTimeInput:59看完本文有收获？请转发分享给更多人
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