單例模式（java，c++，objective-c）

1、java版

單例類 Singleton.java :

public class Singleton {
    private static Singleton instance = null;
                                                                                                                                       
    private Singleton(){
                                                                                                                                           
    }
                                                                                                                                       
    public static Singleton getInstance(){
                                                                                                                                           
        if(instance == null){
            instance = new Singleton();
        }
                                                                                                                                           
        return instance;
    }
}

測試類 Test.java :

public class Test {
    public static void main(String[] args) {
        Singleton singleton = Singleton.getInstance();
        System.out.println(singleton);
                                                                                                                             
        Singleton singleton2 = Singleton.getInstance();
        System.out.println(singleton2);
                                                                                                                             
    }
}

測試結果：

com.hejinlai.singleton.Singleton@6345e044

com.hejinlai.singleton.Singleton@6345e044

2、c++版

單例類 Singleton.h   Singleton.cpp :

//
//  Singleton.h
//  Pattern
//
//  Created by hejinlai on 13-8-6.
//  Copyright (c) 2013年 yunzhisheng. All rights reserved.
//
#ifndef __Pattern__Singleton__
#define __Pattern__Singleton__
#include <iostream>
class Singleton {
                                                                                                 
public:
    static Singleton * getInstance();
                                                                                                 
private:
    Singleton();
    static Singleton * instance;
};
#endif /* defined(__Pattern__Singleton__) */

//
//  Singleton.cpp
//  Pattern
//
//  Created by hejinlai on 13-8-6.
//  Copyright (c) 2013年 yunzhisheng. All rights reserved.
//
#include "Singleton.h"
Singleton * Singleton::instance = NULL;
Singleton::Singleton()
{
                                                                                              
}
Singleton * Singleton::getInstance()
{
    if (instance == NULL) {
        instance = new Singleton();
    }
                                                                                              
    return instance;
}

測試 main.cpp :

//
//  main.cpp
//  Pattern
//
//  Created by hejinlai on 13-8-6.
//  Copyright (c) 2013年 yunzhisheng. All rights reserved.
//
#include <iostream>
#include "Singleton.h"
using namespace std;
int main(int argc, const char * argv[])
{
    Singleton * singleton = Singleton::getInstance();
    cout << singleton << endl;
                                                                 
    Singleton * singleton2 = Singleton::getInstance();
    cout << singleton2 << endl;
                                                                 
    return 0;
}

測試結果：

0x1001000e0

0x1001000e0

3、objective-c 版

單例類 Singleton.h  Singleton.m :

//
//  Singleton.h
//  ObcPattern
//
//  Created by hejinlai on 13-8-6.
//  Copyright (c) 2013年 yunzhisheng. All rights reserved.
//
#import <Foundation/Foundation.h>
@interface Singleton : NSObject
+(Singleton *)getInstance;
@end

//
//  Singleton.m
//  ObcPattern
//
//  Created by hejinlai on 13-8-6.
//  Copyright (c) 2013年 yunzhisheng. All rights reserved.
//
#import "Singleton.h"
static Singleton *instance = nil;
@implementation Singleton
+(Singleton *)getInstance
{
    if (instance == nil) {
        instance = [[self alloc] init];
    }
                            
    return instance;
}
@end

測試 main.m :

//
//  main.m
//  ObcPattern
//
//  Created by hejinlai on 13-8-6.
//  Copyright (c) 2013年 yunzhisheng. All rights reserved.
//
#import <Foundation/Foundation.h>
#import "Singleton.h"
int main(int argc, const char * argv[])
{
    @autoreleasepool {
                     
        Singleton *singleton = [Singleton getInstance];
        NSLog(@"%@", singleton);
                     
        Singleton *singleton2 = [Singleton getInstance];
        NSLog(@"%@", singleton2);
    }
                 
    return 0;
}

測試結果：

2013-08-06 19:43:16.073 ObcPattern[8094:303] <Singleton: 0x1001098b0>

2013-08-06 19:43:16.075 ObcPattern[8094:303] <Singleton: 0x1001098b0>