day15/GenericDemo2.java

本文介绍了Java中泛型类的概念及使用方法。通过对比非泛型类与泛型类的实现方式,阐述了泛型类如何提高代码的复用性和安全性。文章提供了具体的示例代码,展示了泛型类在实际编程中的优势。
/*
泛型类。

*/

class Worker
{
}
class Student
{
}

//泛型前的做法。
class Tool
{
	private	Object obj;
	public void setObject(Object obj)
	{
		this.obj=obj;
	}
	public Object getObject()
	{
		return obj;
	}
}


/*
泛型类。
什么时候定义泛型类?
当类中要操作的引用数据类型不确定的时候,
早期定义Object来完成扩展,
现在定义泛型来完成扩展。
*/
class Utils<QQ>
{
	private QQ q;
	public void setObject(QQ q)
	{
		this.q=q;
	}
	public QQ getObject()
	{
		return q;
	}
}

class GenericDemo2 
{
	public static void main(String[] args) 
	{		
		/*
		Tool t = new Tool();
		t.setObject(new Worker());
		Worker w = (Worker)t.getObject();
		*/

		Utils<Worker> u = new Utils<Worker>();
		u.setObject(new Worker());
		u.getObject();
	}
}

发生了这样的错误org.junit.platform.commons.PreconditionViolationException: Classpath resource [/com/main/nextDay.csv] does not exist at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:215) at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1709) at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:570) at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:560) at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151) at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174) at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:265) at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:636) at java.base/java.util.stream.ReferencePipeline$7$1FlatMap.accept(ReferencePipeline.java:294) at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:215) at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:215) at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:215) at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1709) at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:570) at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:560) at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151) at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174) at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:265) at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:636) at java.base/java.util.stream.ReferencePipeline$7$1FlatMap.accept(ReferencePipeline.java:294) at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1709) at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:570) at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:560) at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151) at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174) at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:265) at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:636) at java.base/java.util.ArrayList.forEach(ArrayList.java:1597) at java.base/java.util.ArrayList.forEach(ArrayList.java:1597) Suppressed: org.junit.platform.commons.PreconditionViolationException: Configuration error: You must configure at least one set of arguments for this @ParameterizedTest at java.base/java.util.stream.AbstractPipeline.close(AbstractPipeline.java:355) at java.base/java.util.stream.ReferencePipeline$7$1FlatMap.accept(ReferencePipeline.java:289) ... 9 more
03-24
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