使用同步机制将单例模式中的懒汉式改写为线程安全的
原代码：不安全
package com.dxc;
public class BankTest {
}
class Bank {
private Bank() {
}
private static Bank instance = null;
public static Bank getInstance(){
if (instance == null){
instance = new Bank();
}
return instance;
}
}
修改1：安全，此时静态的同步方法是类本身
package com.dxc;
public class BankTest {
}
class Bank {
private Bank() {
}
private static Bank instance = null;
//synchronized
public static synchronized Bank getInstance(){
if (instance == null){
instance = new Bank();
}
return instance;
}
}
修改2：安全
- 方式一：synchronized包裹，效率稍差
package com.dxc;
public class BankTest {
}
class Bank {
private Bank() {
}
private static Bank instance = null;
public static Bank getInstance(){
//方式一：效率稍差
synchronized (Bank.class) {
if (instance == null){
instance = new Bank();
}
return instance;
}
}
}
- 方式二：优化（加一层if）
package com.dxc;
public class BankTest {
}
class Bank {
private Bank() {
}
private static Bank instance = null;
public static Bank getInstance(){
//方式二：加一层if
if (instance == null) {
synchronized (Bank.class) {
if (instance == null) {
instance = new Bank();
}
}
}
return instance;
}
}
