單例模式的幾種實現方式
/**考察知識點單例及Spring Bean的單例設計*/
class Singleton01{
private Singleton01() {}
private static Singleton01 instance;
public static Singleton01 getInstance() {
if(instance==null) {
instance=new Singleton01();
}
return instance;
}
}
class Singleton02{//適合大對象,稀少用
private Singleton02() {}
private static Singleton02 instance;
public synchronized static Singleton02 getInstance() {
if(instance==null) {
instance=new Singleton02();
}
return instance;
}
}
class Singleton03{//適合大對象(合適需要合適加載),稀少用
private Singleton03() {}
private static volatile Singleton03 instance;
public static Singleton03 getInstance() {
if(instance==null) {
synchronized (Singleton03.class) {
if(instance==null) {
instance=new Singleton03();
}
}
}
return instance;
}
}
class Singleton04{//小對象,頻繁用
//int[] n=new int[1024];
private Singleton04() {}
private static Singleton04 instance=new Singleton04();
public static Singleton04 getInstance() {
return instance;
}
public static void display() {}
}
class Singleton05{//對04進行優化
private Singleton05() {}
static class Inner{//延遲加載策略
private static Singleton05 instance=
new Singleton05();
}
public static Singleton05 getInstance() {
return Inner.instance;
}
public static void display() {}
public void show() {}
}
enum Singleton06{
instance;
public static void display() {}
}
class Singleton01{
private Singleton01() {}
private static Singleton01 instance;
public static Singleton01 getInstance() {
if(instance==null) {
instance=new Singleton01();
}
return instance;
}
}
class Singleton02{//適合大對象,稀少用
private Singleton02() {}
private static Singleton02 instance;
public synchronized static Singleton02 getInstance() {
if(instance==null) {
instance=new Singleton02();
}
return instance;
}
}
class Singleton03{//適合大對象(合適需要合適加載),稀少用
private Singleton03() {}
private static volatile Singleton03 instance;
public static Singleton03 getInstance() {
if(instance==null) {
synchronized (Singleton03.class) {
if(instance==null) {
instance=new Singleton03();
}
}
}
return instance;
}
}
class Singleton04{//小對象,頻繁用
//int[] n=new int[1024];
private Singleton04() {}
private static Singleton04 instance=new Singleton04();
public static Singleton04 getInstance() {
return instance;
}
public static void display() {}
}
class Singleton05{//對04進行優化
private Singleton05() {}
static class Inner{//延遲加載策略
private static Singleton05 instance=
new Singleton05();
}
public static Singleton05 getInstance() {
return Inner.instance;
}
public static void display() {}
public void show() {}
}
enum Singleton06{
instance;
public static void display() {}
}
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