# Java笔记

**Repository Path**: yqw123/JavaBiJi

## Basic Information

- **Project Name**: Java笔记
- **Description**: 开发过程中java的一些使用技巧总结
- **Primary Language**: Java
- **License**: EPL-1.0
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2017-11-04
- **Last Updated**: 2021-04-18

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# Java笔记

## 个人简介


## 泛型新玩法
- 泛型技巧`ConcurrentMap<String, String> newConcurrentMap = Maps.<String, String>newConcurrentMap();`

```
	@Test
	public void mapTest() {
		LinkedHashMap<String, String> newConcurrentMap = Maps.<String, String>newLinkedHashMapWithExpectedSize(1);
		System.out.println("mapTest: " + newConcurrentMap);
	}
	//打印结果：mapTest: {}
	
	@Test
	public void createMapTest() {
		LinkedHashMap<String, String> newConcurrentMap = Maps.<String, String>newLinkedHashMapWithExpectedSize(1);
		System.out.println("createMapTest: " + newConcurrentMap);
	}
	//打印结果：createMapTest: {}
```

## 接口实现类之枚举实现巧用

```
  enum NullListener implements RemovalListener<Object, Object> {
    INSTANCE;

    @Override
    public void onRemoval(RemovalNotification<Object, Object> notification) {}
  }

  enum OneWeigher implements Weigher<Object, Object> {
    INSTANCE;

    @Override
    public int weigh(Object key, Object value) {
      return 1;
    }
  }
```

## Map- put技巧

```
		Map<Integer, String> putIfAbsent = new HashMap<>();
		System.out.println(putIfAbsent.put(1, "张三"));
		System.out.println(putIfAbsent.putIfAbsent(2, "李四"));
		System.out.println("put==" + putIfAbsent.put(2, "丁力"));
		System.out.println("put==" + putIfAbsent.put(2, "丁力"));
		System.out.println("putIfAbsent==" + putIfAbsent.putIfAbsent(1, "王五"));
		System.out.println("putIfAbsent==" + putIfAbsent.putIfAbsent(1, "王五"));
		putIfAbsent.forEach((key,value)->{
			System.out.println("key = " + key + ", value = " + value);
		});
```

## Maven命令行窗口指定settings.xml

maven命令行窗口指定特定settings.xml ，在命令行界面指定settings.xml，需加入如下参数：

```
//指定使用配置xml编译项目
mvn install --settings d:\maven\conf\settings.xml 
mvn install -s d:\maven\conf\settings.xml 
 
//指定使用配置xml编译项目 并忽略单元测试代码
mvn clean package --settings d:\maven\conf\\settings.xml -Dmaven.test.skip=true
mvn clean package -s d:\maven\conf\\settings.xml -Dmaven.test.skip=true




- Maven查看当前生效的settings.xml
用mvn help:effective-settings可以查看当前生效的settings.xml：
mvn -X命令可以查看settings.xml文件的读取顺序：

总结：
maven-help-plugin是一个小巧的辅助工具，
最简单的mvn help:system可以打印所有可用的环境变量和Java系统属性。
mvn help:effective-pom和mvn help:effective-settings最为有用。
mvn help:effective-pom用于查看当前生效的POM内容，指合并了所有父POM（包括Super POM）后的XML，所以可用于检测POM中某个配置是否生效
mvn effective-settings可用于查看当前生效的settings.xml文件内容，所以可用于判断某个settings配置是否生效



```
[maven全局配置文件settings.xml详解](https://www.cnblogs.com/jingmoxukong/p/6050172.html?utm_source=gold_browser_extension)