JAVA8跳出循环 |
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文章目录
概述普通循环fori循环for循环
forEach循环Iterable.forEach循环 —— by MutableBooleanStream.forEach —— by anyMatchStream.forEach —— by findAny
附录MutableBoolean
参考
概述
我们都知道continue、break用在哪里，怎么用以及用来干啥，即 continue 用于循环体内 用来结束本次循环 break 用于循环体内 用来跳出循环 但是，forEach有些特殊，上面的关键字并不能在forEach循环体内直接用，否则会编译不通过，具体报错为 break outside switch or loop或 continue outside of loop 普通循环 fori循环collection、map、Map.Entry的循环也类似，这里不再赘述 //example 1 int[] intArr = new int[]{1,2,3,4,5,6,7,8,9,10}; StringBuilder content = new StringBuilder(16); for (int i = 0; i continue;} //结束循环 if(item == 8){ break;} content.append(item); } Assert.assertEquals("哦豁，写bug了吧","123467",content.toString()); for循环collection、map、Map.Entry的循环也类似，这里不再赘述 //example2 int[] intArr = new int[]{1,2,3,4,5,6,7,8,9,10}; StringBuilder content = new StringBuilder(16); for (int item : intArr) { //跳出本次循环，继续下一轮循环 if(item == 5){ continue;} //结束循环 if(item == 8){ break;} content.append(item); } Assert.assertEquals("哦豁，写bug了吧","123467",content.toString()); forEach循环 Iterable.forEach循环 —— by MutableBoolean //example 3 //注1 用continue会报错，并提示：continue outside of loop //注2 用break会报错，并提示：break outside switch or loop //注1 return实现continue的效果 //注2 用try-catch实现break效果 Collection c = Arrays.asList(1,2,3,4,5,6,7,8,9,10); StringBuilder content = new StringBuilder(16); try { c.forEach((item) -> { if (item == 5) {return;} if (item == 8) { throw new RuntimeException("不用再继续循环了"); }else{ content.append(item); } }); } catch (RuntimeException ex) { } Assert.assertEquals("哦豁，写bug了吧","123467",content.toString());用try-catch这种抛异常的方式来跳出循环确实太挫了(代码不简洁不美观、且使用场景不太对，毕竟异常是意料之外，而这个跳出循环是正常的一种程序应用场景)，在看看下面这种MutableBoolean方式 //example 4 //collection: MutableBoolean来实现break功能; return实现continue //注1 MutableBoolean的定义方式见附录 Collection c = Arrays.asList(1,2,3,4,5,6,7,8,9,10); StringBuilder content = new StringBuilder(16); final MutableBoolean mutableBoolean = new MutableBoolean(true); c.forEach((item) -> { if (item == 5) {return;} if (item == 8) { mutableBoolean.setFlag(Boolean.FALSE); }else if(mutableBoolean.getFlag()) { content.append(item); } }); Assert.assertEquals("哦豁，写bug了吧","123467",content.toString());see 是不是elegant、简洁多了。在看看Map的方式，其实也是一模一样的 StringBuilder content = new StringBuilder(16); final MutableBoolean mutableBoolean = new MutableBoolean(true); Map map = new HashMap(16); for (int i = 0; i if (v == 5) {return;} if (v == 8) { mutableBoolean.setFlag(Boolean.FALSE); }else if(mutableBoolean.getFlag()) { content.append(v); } }); Assert.assertEquals("哦豁，写bug了吧","123467",content.toString()); Stream.forEach —— by anyMatch一种是anyMatch //example 6 //stream: anyMatch跳出循环; return false 实现continue Collection c = Arrays.asList(1,2,3,4,5,6,7,8,9,10); StringBuilder content = new StringBuilder(16); c.stream().anyMatch((item)->{ if (item == 5) {return false;} boolean flag = 8 == item; if(!flag) { content.append(item); } return flag; }) ; Assert.assertEquals("哦豁，写bug了吧","123467",content.toString()); Stream.forEach —— by findAny //example 7 //stream: findAny跳出循环; return false 实现continue Collection c = Arrays.asList(1,2,3,4,5,6,7,8,9,10); StringBuilder content = new StringBuilder(16); c.stream().filter((item)->{ if (item == 5) {return false;} boolean flag = 8 == item; if(!flag) { content.append(item); } return flag; }).findAny() ; Assert.assertEquals("哦豁，写bug了吧","123467",content.toString()); 附录 MutableBoolean /** * 可变布尔变量 */ static class MutableBoolean{ //标记 private Boolean flag; public MutableBoolean(Boolean flag) { this.flag = flag; } public Boolean getFlag() { return flag; } public void setFlag(Boolean flag) { this.flag = flag; } } 参考 Java8中的foreach跳出循环break/return |
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